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AGRICULTURE 


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UNIVERSITY    OF    ILLINOIS    LIBRARY    AT    URBANA-CHAMPAIGN 


L161— O-1096 


UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  278 


THE  GROWTH  OF  WHITE  PLYMOUTH 
ROCK  CHICKENS 


BY  H.  H.  MITCHELL,  L.  E.  CARD, 
and  T.  S.  HAMILTON 


A  significant  indication  of  the  probable  future  profitableness  of 
a  flock  of  chickens  is  the  way  in  which  they  grow.  It  is  therefore 
important  to  find  out  the  form  and  quantity  in  which  the  essen- 
tial nutrients  must  be  supplied  to  support  maximum  growth. 


URBANA,  ILLINOIS,  JUNE,  1926 


CONTENTS 

INTRODUCTION 71 

DESCRIPTION  OF  THE  EXPERIMENT 73 

EXPERIMENTAL  RESULTS 75 

Increase  in  Body  Measurements  with  Age 77 

Surface  Area  of  the  Birds  at  Different  Ages 80 

Relative  and  Absolute  Growth  of  the  Different  Parts  of  the  Carcass  and 
Viscera 87 

Chemical  Composition  of  the  Birds  at  Different  Weights 100 

Rate  of  Retention  of  Nutrients  During  Growth 114 

SUMMARY  AND  CONCLUSIONS 124 

LITERATURE  CITED 123 

APPENDIX..  .  129 


THE  GROWTH  OF  WHITE  PLYMOUTH 
ROCK  CHICKENS 

BY  H.  H.  MITCHELL,  L.  E.  GAUD,  and  T.  S.  HAMILTON" 

The  rate  and  manner  in  which  a  given  species  of  animal  grows, 
besides  being  of  great  physiological  importance,  must  form  the  basis 
for  any  estimation  of  the  nutrient  requirements  for  that  species.  It  is 
also  important  that  the  practical  animal  husbandman  know  some- 
thing of  the  normal  growth  of  the  animals  which  he  is  raising,  in  order 
that  he  may  judge  the  success  of  his  own  feeding  operations. 

The  most  scientific  method  of  estimating  the  food  requirements 
of  any  species  of  animal  for  growth  is  undoubtedly  the  system  devel- 
oped by  Armsby  relative  to  the  energy  requirements.  According  to, 
this  system  an  estimate  of  the  amount  of  energy  that  animals  need  at! 
different  stages  of  growth  must  be  based  upon  reliable  information 
relating  to  three  distinct  points:  first,  the  maintenance  requirement  of 
the  animals  at  different  stages  of  growth;  second,  the  normal  rate  of 
increase  in  body  weight  during  the  growing  period ;  and  third,  the  com- 
position of  the  gains  put  on  at  different  ages.  Furthermore,  in  order  i 
to  make  practical  use  of  this  information  in  the  formulation  of  feed-  ' 
ing  standards  for  growth,  it  is  necessary  to  know  the  extent  of  the  util- 
ization of  food  energy  by  growing  animals  at  different  ages.  This 
system  has  been  developed  by  Armsby  only  in  connection  with  energy 
requirements  and  the  energy  values  of  feeds.  There  is  every  reason 
to  suppose,  however,  that  the  system  could  be  extended  to  include  other 
nutrients  such  as  protein  and  mineral  matter,  by  obtaining  for  each 
nutrient  information  analogous  to  that  just  indicated  with  reference 
to  energy. 

The  production  of  meat  by  growing  animals  is  most  commonly 
measured  simply  by  the  increase  in  weight.  However,  the  increase  in). 
weight  at  different  ages  is  known  to  vary  widely  in  composition.  For 
example,  a  pound  of  protoplasm  such  as  a  young  animal  would  put  on 
during  growth  has  an  energy  value  of  about  500  calories  and  a  pro- 
tein content  of  approximately  20  percent.  As  the  age  of  the  animal 
increases,  the  water  content  of  its  gains  decreases  and  the  nature  of 
the  solid  matter  changes  progressively,  due  to  an  increasing  proportion 
of  fat.  In  the  last  stages  of  fattening,  a  pound  increase  in  weight  may 
have  an  energy  value  of  4,000  calories,  and  may  contain  only  a  mere 


aH.  H.  MITCHELL,  Chief  in  Animal  Nutrition;  L.  E.  CARD,  Chief  in  Poultry 
Husbandry;  T.  S.  HAMILTON,  Associate  in  Animal  Nutrition. 

71 


72  BULLETIN  No.  278  [June, 

trace  of  protein.  It  is  quite  evident  that  as  this  change  in  composi- 
tion of  gains  takes  place  the  food  required  to  produce  these  gains  will 
increase  in  amount  and  change  progressively  in  quality. 

Among  practical  livestock  men  it  may  not  be  generally  realized 
that  the  composition  of  gains  put  on  by  meat  animals  varies  as  widely 
as  this.  Even  when  it  is  realized  that  such  differences  do  occur,  little 
practical  use  can  be  made  of  this  knowledge  since  precise  information 
is  not  available  regarding  the  composition  of  the  gains  which  animals 
put  on  at  different  ages. 

In  dairy  production  it  is  well  known  that  the  productive  capacity 
of  a  cow  is  measured  not  only  by  the  amount  of  milk  she  will  produce 
but  also  by  its  composition.  Since  in  this  case  the  product  can  be  so 
readily  removed  from  the  animal  and  submitted  to  analysis,  many 
thousands  of  analyses  of  milk  of  different  grades  have  been  made  with 
various  purposes  in  view,  and  have  been  reported  in  the  literature  of 
the  subject.  At  the  present  time  any  thorogoing  feeding  standard  for 
milk  production  considers  not  only  the  amount  of  milk  produced  but 
also  its  composition,  particularly  in  energy  or  total  nutrients.  Never- 
theless, the  need  for .  considering  the  composition  of  the  product  in 
milk  production  is  not  so  urgent  as  in  meat  production,  because  of  the 
narrower  range  in  the  composition  of  milk  as  compared  with  the  com- 
position of  gains  put  on  by  growing  and  fattening  animals.  A  pound 
of  milk  testing  2.5  percent  fat,  for  example,  has  an  energy  value  of  a 
little  over  half  that  of  a  pound  of  milk  testing  7  percent  fat,  while  a 
pound  of  gain  put  on  by  a  young  animal  may  have  an  energy  value 
of  only  one-eighth  that  of  a  pound  of  gain  put  on  by  an  animal  in  the 
last  stages  of  fattening. 

The  most  efficient  method  for  determining  the  composition  of  the 
gains  of  growing  animals  is  to  slaughter  animals  at  different  ages  and 
weights  and  submit  their  carcasses  to  a  careful  chemical  examination. 
From  such  data  the  composition  of  gains  between  two  different  weights 
may  be  computed  by  assuming  that  the  animals  slaughtered  at  the 
higher  weight  had  the  same  composition  at  the  lower  weight  as  the 
animals  actually  killed  at  that  weight.  While  a  considerable  number 
of  analyses  of  the  different  farm  animals  at  different  ages  and  weights 
may  be  found  in  the  literature,  the  number  is  still  insufficient  in  many 
cases  to  form  the  basis  of  a  reliable  feeding  standard.  For  example, 
in  arriving  at  his  estimate  of  the  energy  requirements  of  growing  pigs, 
Armsby  has  sought  for  information  concerning  the  energy  content  of 
a  pound  increase  in  weight  put  on  by  pigs  at  birth  and  at  an  age  when 
growth  may  be  assumed  to  have  been  practically  complete.  The 
change  in  composition  between  these  two  ages  is  then  assumed  to  vary 
in  a  linear  fashion  with  age.  While  the  experimental  information  on 
the  composition  of  the  early  gains  is  fairly  satisfactory,  the  informa- 
tion relative  to  the  energy  value  of  gains  put  on  at  18  to  24  months  of 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS  73 

age  consisted  of  determinations  by  Soxlet  on  two  pigs  16.5  months  of 
age.  One  value  was  1,401  calories  per  pound,  the  other  was  2,485 
calories  per  pound.  Since  the  latter  value  was  more  consistent  with 
similar  data  on  other  animals,  it  was  chosen  in  preference  to  the 
former,  but  it  is  evident  that  much  more  complete  information  on  this 
point  should  be  obtained. 

No  information  is  available  in  the  literature  from  which  the  com- 
position of  gains  put  on  by  growing  poultry  may  be  computed.  Very 
little  is  known  of  the  maintenance  requirement  of  poultry  or  of  the 
difference  in  maintenance  requirement  between  the  different  sexes.  The 
extent  to  which  poultry  utilize  the  energy  of  their  feeds  is  also  practic- 
ally unknown,  so  that  the  formulation  of  a  scientific  estimate  of  the 
food  requirements  of  growing  chickens  is  impossible  at  the  present 
time.  The  experiment  reported  in  this  bulletin  is  the  first  of  a  series 
of  investigations  that  is  being  undertaken  by  the  Nutrition  and  Poul- 
try Divisions  of  the  Illinois  Agricultural  Experiment  Station  to  obtain 
information  upon  which  feeding  standards  for  poultry  may  be  based. 


DESCRIPTION  OF  THE  EXPERIMENT 

The  object  of  the  experiment  reported  in  this  bulletin  was  to  in- 
vestigate the  growth  of  White  Plymouth  Rock  chickens  by  measuring 
the  increase  of  size  of  the  entire  bird  and  of  individual  organs  for 
pullets,  cockerels,  and  capons,  and  by  determining  the  composition  of 
the  gains  in  weight  put  on  at  different  ages. 

A  flock  of  approximately  1,000  White  Plymouth  Rock  chicks 
hatched  March  28,  1923,  was  used  in  this  investigation.  They  were 
range-reared  on  the  colony  house  plan  at  the  poultry  farm,  and  were 
fed  the  standard  ration  used  at  this  Station  for  growing  birds.  Indi- 
vidual weights  of  the  birds  were  taken  every  two  weeks.  When  the 
flock  reached  an  average  weight  of  about  1.5  pounds,  the  cockerels  and 
pullets  were  separated  and  approximately  half  the  cockerels  were 
caponized.  From  this  time  on  they  were  fed  in  three  groups — pullets, 
cockerels,  and  capons. 

Groups  of  birds  were  removed  according  to  weight  rather  than 
age,  for  measurement,  slaughter,  and  analysis.  Five  chicks  were  se- 
lected from  the  entire  flock  at  weights  of  .5  pound,  1  pound,  and  1.5 
pounds,  these  selections  including  only  cockerels  in  so  far  as  the  sex 
could  be  distinguished.  To  determine  whether  the  measurements  and 
composition  of  the  birds  were  greatly  affected  by  age,  when  killed  at 
the  same  weight,  two  groups  of  5  chicks  each,  differing  by  two  weeks 
in  age,  were  slaughtered  at  the  1 -pound  weight. 

At  the  2-pound  weight  two  groups  of  5  birds  each  were  selected 
for  slaughter,  one  consisting  of  5  pullets  and  the  other  of  5  cockerels. 


74  BULLETIN  No.  273  [June, 

s 

From  this  weight  on,  the  selections  of  birds  were  made  at  intervals  of 
1  pound.  Starting  with  a  weight  of  3  pounds,  5  pullets,  5  cockerels, 
and  5  capons  were  selected  for  measurement  and  slaughter.  At  1- 
pound  intervals  thereafter  the  growth  of  pullets  was  studied  up  to  a 
weight  of  5  pounds,  and  the  growth  of  cockerels  and  capons  up  to  a 
weight  of  7  pounds. 

The  following  measurements  were  made  on  all  birds  removed  for 
slaughter: 

1.  Depth  from  front  end  of  keel  bone  to  back 

2.  Depth  from  rear  end  of  keel  bone  to  back 

3.  Length  from  rump  to  tip  of  beak 

4.  Length  from  rump  to  shoulder 

5.  Circumference  of  trunk  just  behind  wings 

6.  Length  of  shank 

7.  Length  of  middle  toe 

8.  Length  of  drumstick 

9.  Length  of  keel  bone 

10.  Breadth  from  hip  to  hip 

The  birds  were  then  killed,  bled,  and  dry  picked.  The  skins  were 
removed  and  their  areas  determined.  The  carcasses  were  then  cut 
up  and  fresh  weights  of  the  following  portions  were  taken: 

1.  Blood  13.  Pancreas 

2.  Feathers  14.  Spleen 

3.  Head  15.  Lungs 

4.  Shanks  and  feet  16.  Testicles  (in  cockerels) 

5.  Skin  17.  Gullet  and  proventriculus 
r}'    6.  Neck  18.  Gizzard 

7.  Legs  above  hock  19.  Intestinal  tract 

8.  Wings  20.  Contents  of  gizzard 

9.  Torso  21.  Contents  of  intestinal  tract 

10.  Heart  22.  Total  bones  in  dressed  carcass 

11.  Liver  23.  Total  flesh  in  dressed  carcass 

12.  Kidneys' 

The  length  of  the  intestinal  tract  in  each  bird  was  also  measured. 

For  each  group  of  5  birds  the  following  three  composite  samples 
were  made  up  for  analysis: 

1.  All  bones,  except  those  in  head,  shanks,  and  feet 

2.  Flesh,  heart,  liver,  and  gizzard 

3.  Offal,  including  the  blood,  feathers,  head,  shanks  and  feet,  skin,  and  all 
viscera  not  included  in  the  second  sample 

Each  of  these  three  samples  was  ground  fresh,  preserved  with  exactly 
1  percent  of  thymol  (a  correction  for  which  was  made  in  reporting  the 
analyses),  and  analyzed  in  a  fresh  condition  for  moisture,  nitrogen, 
ether  extract,  and  ash.  The  gross  energy  of  each  sample  was  directly 
determined  in  the  bomb  calorimeter. 


'The  kidneys  were  not  weighed  in  the  .5-pound  chicks. 


1926']  THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 

EXPERIMENTAL  RESULTS 


73 


The  flock  of  White  Plymouth  Rock  chickens  from  which  birds 
were  taken  for  measurement  and  analysis  was  weighed  at  bi-weekly 
intervals.  The  weights  thus  obtained  are  compiled  in  Table  1.  The 
weight  of  46  grams  given  as  the  hatching  weight  of  the  chicks  is  actu- 
ally the  weight  of  the  chicks  at  two  days  of  age.  The  birds  were  ob- 
tained from  a  commercial  hatchery  and  were  weighed  immediately 


TABLE  1. — BIWEEKLY  WEIGHTS  OF  THE  WHITE  PLYMOUTH  ROCK  CHICKENS 
USED  IN  THIS  STUDY 


Age 

Cockerels 

Pullets 

Capons 

Number 
of 
birds 

Aver- 
age 
weight 

Biweekly 
increase 
in  weight 

Number 
of 
birds 

Aver- 
age 
weight 

Biweekly 
increase 
in  weight 

Number 
of 
birds 

Aver- 
age 
weight 

Biweekly 
increase 
in  weight 

wks. 

gms. 

gms. 

gms. 

gms. 

gms. 

gms. 

0 

46 

46 

?, 

400 

87 

41 

507 

85 

39 

4 

401 

178 

91 

502 

163 

78 

6 

401 

308 

130 

493 

280 

117 

8 

399 

477 

169 

472 

416 

136 

10 

391a 

605 

128 

420 

535 

119 

12 

184 

716 

111 

384 

602 

67 

150 

675 

70 

14 

178 

907 

191 

363 

752 

150 

135 

892 

217 

16 

170 

1  150 

243 

353 

919 

167 

139 

1  095 

210 

18 

163 

1  229 

79 

322 

1  036 

117 

129 

1  271 

176 

20 

152 

1  347 

118 

312 

1  140 

104 

129 

1  379 

108 

22 

145 

1  557 

210 

293 

1  285 

145 

119 

1  658 

279 

24 

135 

1  636 

79 

281 

1  403 

118 

108 

1  849 

191 

26 

118 

1  756 

120 

267 

1  533 

130 

113 

1  899 

50 

28 

116 

1  962 

206 

247 

1  647 

114 

74 

2  206 

307 

30 

112 

2  135 

173 

230 

1  734 

89 

77 

2  330 

124 

32 

116 

2  062 

-73 

223 

1  774 

40 

74 

2  371 

41 

34 

93 

2  515 

453 

200 

2  025 

251 

67 

2  449 

78 

36 

69 

2  536 

21 

186 

2  005 

-20 

43 

2  385 

-64 

38 

70 

2  623 

87 

39 

2  497 

112 

40 

67 

2  798 

175 

39 

2  587 

90 

4?, 

64 

2  744 

-54 

42 

2  516 

-71 

44 

62 

2  804 

60 

37 

2  679 

163 

46 

46 

2  778 

-26 

29 

2  759 

80 

"Approximately  half  the  cockerels  were  caponized  at  this  time. 

on  arrival  at  Urbana.  The  decrease  in  numbers  of  birds  indicated  in 
the  table  was  due  not  only  to  mortality,  but  also  to  the  fact  that  birds 
were  removed  from  this  flock  at  various  times  for  purposes  other  than 
those  of  this  experiment. 

A  comparison  of  the  growth  rate  of  these  White  Plymouth  Rock 
chickens  with  that  recorded  by  Philips2  shows  that  the  growth  obtained 
in  this  experiment  was  considerably  slower  and  less  sustained  than  that 
obtained  at  Purdue.  In  addition  to  the  fact  that  these  chicks  appear 
to  have  come  from  a  rather  small  strain  of  White  Plymouth  Rocks,  it 


76 


BULLETIN  No.  278 


[June, 


G 


o  5 
UCQ 


PH 


w  « 

pj  53 


a 

o 

CQ 

H 

O 

H 


Approximate  slaughte 
weigh 


"*  CO 
(N  "3 
CO  (N 


OCO 

55 
N 


§§  *•.-. 


i-H  i-(          ^H  COIN 


~H  CO 

r^t^ 

o 


1> 

CO-* 


§: 


§-S 

i-i  ^J 

1§ 


s 

3  bO 


HHTHiftsl  "^ 

%  i   <t_i 

o 


e  o ..  . 
1-0° 
&b  g^ 


.2 


3  1 

u 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


77 


should  be  pointed  out  that  the  environment  under  which  they  were 
reared  was  not  ideal.  The  range  area  in  use  contained  no  natural 
shade  and  artificial  straw  shelters  had  to  be  constructed.  The  lack  of 
shade  probably  was  partly  responsible  for  the  rather  slow  rate  of 
growth  obtained. 

From  two  weeks  of  age  on  the  cockerels  increased  in  weight  at  a 
more  rapid  rate  than  the  pullets  (Table  1).  No  clear  difference  in 
growth  is  apparent  between  cockerels  and  capons,  except  for  a  slightly 
more  rapid  growth  of  the  capons  from  the  18th  to  the  32d  week. 

The  biweekly  increases  in  weight  exhibit  what  might  be  called  a 
cyclic  tendency,  it  will  be  noted  from  Table  1.  The  authors  hesitate 
to  attach  much  significance  to  these  cycles.  While  there  is  a  tendency 
to  interpret  such  changes  in  the  rate  of  growth  as  indicating  "cycles  of 
growth,"  such  an  interpretation  fails  to  consider  important  environ- 
mental factors.  The  weather,  particularly,  may  exhibit  periodic  var- 
iations and  these  very  probably  exert  a  pronounced  effect  on  the 
growth  of  the  animals.  The  discussion  of  this  point  will  be  resumed  in 
a  later  section  of  the  bulletin. 

INCREASE  IN  BODY  MEASUREMENTS  WITH  AGE 

The  average  body  measurements  of  the  several  groups  of  birds  re- 
moved at  different  weights  are  given  in  Tables  2,  3,  and  4.  These 


TABLE  3. — AVERAGE  BODY  MEASUREMENTS  OF  WHITE  PLYMOUTH  ROCK  PULLETS 

AT  DIFFERENT  WEIGHTS:  EACH  FIGURE  Is  AN  AVERAGE  OF  FIVE  BIRDS 

(All  measurements  are  in  centimeters) 


Approximate  slaughter  weight  

2 

3 

4 

5 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Age  in  days  

73 

94 

189 

219 

Live  weight  in  grams  

961 

1  342 

1  842 

2  340 

Depth  at  front  end  of  keel  

9  3 

10  7 

11  6 

12  4 

Depth  at  rear  end  of  keel  

9  0 

10  1 

11  1 

12  5 

Length  of  keel  

8.9 

10.3 

11.9 

12.7 

Length  of  drumstick  

13.0 

15.0 

15.2 

15.8 

Length  of  shank  

10.0 

11.1 

10.9 

11.6 

Length  of  middle  toe  

7.0 

7.5 

7.1 

7.6 

Rump  to  shoulder  

16.2 

18.0 

18.8 

19.5 

Length  over  all  

35.0 

39.0 

40.0 

41.0 

Mid-circumference  

25.0 

29.0 

33.0 

36.0 

Breath  at  hips  

6.4 

7.8 

8.1 

8.9 

tables  also  include  the  average  live  weight  in  grams  and  the  age  in 
days.  Each  group  of  birds  includes  5  individuals,  except  the  group 
removed  at  approximately  1  pound  in  weight,  which  includes  two  lots 
of  birds  measured  at  dates  two  weeks  apart.  The  measurements  for 


78 


BULLETIN  No.  278 


[June, 


these  two  lots  at  the  same  weight  were  so  nearly  the  same  that  they 
have  been  averaged  together.* 

The  change  in  size  of  the  birds  as  indicated  by  these  measure- 
ments may  be  studied  to  best  advantage  probably  by  expressing  the 
average  measurements  at  increasing  weights  in  percentage  of  the  cor- 
responding measurement  of  the  .5-pound  chicks.  This  has  been  done 
for  the  cockerels  as  shown  in  Table  5,  which  also  includes  values  re- 
lating to  body  surface.  Practically  all  of  the  measurements  taken  on 
these  birds  increased  in  approximately  the  same  proportion  when  re- 
ferred to  the  measurements  of  the  .5-pound  chicks.  Thus,  for  all  of 
the  measurements  except  the  length  of  middle  toe  the  7-pound  cock- 


TABLE  4. — AVERAGE  BODY  MEASUREMENTS  OP  WHITE  PLYMOUTH  ROCK  CAPONS 

AT  DIFFERENT  WEIGHTS:  EACH  FIGURE  Is  AN  AVERAGE  OF  FIVE  BIRDS 

(All  measurements  are  in  centimeters) 


Approximate  slaughter  weight  

3 
Ibs. 

4 
Ibs. 

5 
Ibs. 

6 
Ibs. 

7 
Ibs. 

Age  in  davs  

88 

170 

180 

215 

240 

Live  weight  in  grams  

1  375 

1  702 

2  285 

2  684 

3  188 

Depth  at  front  end  of  keel  

11.0 

12  3 

13.2 

13.2 

13.4 

Depth  at  rear  end  of  keel  

10  2 

10  8 

12  3 

12  2 

13  4 

Length  of  keel  

9  7 

11  1 

12  1 

13  0 

13  5 

Length  of  drumstick  

15  3 

17  1 

18  4 

18  5 

18  2 

Length  of  shank  

11  7 

12  6 

13  8 

13  5 

13  4 

Length  of  middle  toe  

7  9 

8  0 

8  7 

8  4 

8  7 

Rump  to  shoulder  

17  8 

19  8 

20  6 

22  2 

21  9 

Length  over  all  

39  0 

45  0 

44  0 

47  0 

46  0 

Mid-circumference  

29  0 

30  0 

35  0 

37  0 

40.0 

Breadth  at  hips  

7.8 

8.4 

8.7 

9.4 

9.8 

erels  were  approximately  2.5  times  as  large  as  the  .5-pound.  This  can 
be  interpreted  to  mean  that  the  conformation  of  the  birds  did  not 
change  materially  during  the  whole  course  of  growth  from  .5  pound  to 
7  pounds  in  weight.  The  body  weight  itself,  of  course,  increased  much 
more  rapidly  when  computed  in  this  way  than  did  the  body  measure- 
ments, while  the  body  surface,  as  would  be  expected,  increased  much 


•The  average  measurements  of  these  two  groups  of  birds  removed  at  a 
weight  of  approximately  1  pound,  but  at  an  interval  of  two  weeks,  were  as  fol- 
lows: 

(Body  measurements  in  centimeters) 


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6.9 

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11.9 

THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


79 


less  rapidly  than  did  the  body  weight.  The  increase  in  size  of  the  pul- 
lets and  capons  may  be  studied  by  a  slightly  different  method,  as  ex- 
emplified in  Tables  6  and  7.  In  these  tables  the  body  measurements 
of  pullets  and  capons  of  different  weights  have  been  expressed  as  per- 
centages of  the  corresponding  measurements  of  cockerels  of  the  same 
weight.  In  this  way,  differences  in  the  conformation  of  these  two 
groups  of  birds  as  compared  to  the  cockerels  have  been  brought  out. 


TABLE   5. — RELATIVE  INCREASE   IN   BODY  WEIGHT,   BODY  SURFACE,   AND   BODY 
MEASUREMENTS  OF  WHITE  PLYMOUTH  ROCK  COCKERELS  DURING  GROWTH 


Approximate  slaughter 
weight  

0.5 
Ib. 

1 
Ih 

1.5 
Ibs. 

2 
Ibs. 

3 
Ibs. 

4 
Ibs. 

5 

Ibs. 

6 
.Ibs. 

7 
Ibs. 

BODY  WEIGHT  

100 

194 

290 

428 

587 

769 

964 

1  113 

1  402 

BODY  SURFACE  

100 

193 

279 

369 

452 

549 

659 

731 

814 

BODY  MEASUREMENTS 
Depth  at  front  end  of 
keel  

100 

132 

160 

183 

206 

236 

247 

253 

257 

Depth  at  rear  end  of 
keel  

100 

136 

158 

165 

191 

204 

213 

229 

251 

Length  of  keel  

100 

134 

160 

186 

206 

234 

244 

262 

278 

Length  of  drumstick  .  .  . 
Length  of  shank  

100 
100 

131 
130 

160 
158 

194 
200 

217 
215 

250 
245 

263 
260 

261 
257 

263 
257 

Length  of  middle  toe.  . 
Rump  to  shoulder  
Length  over  all  

100 
100 
100 

125 
130 
130 

145 
152 
148 

177 
184 
184 

184 
201 
204 

186 
218 
224 

205 
236 
230 

193 
240 
245 

205 
242 
246 

Mid-circumference.  .  .  . 
Breadth  at  hips  

100 
100 

134 
127 

150 
141 

179 
163 

203 
183 

224 
215 

245 
222 

259 
234 

266 
256 

TABLE  6. — AVERAGE  BODY  MEASUREMENTS  OF  WHITE  PLYMOUTH  ROCK  PULLETS  AT 

DIFFERENT  WEIGHTS,  EXPRESSED  AS  PERCENTAGES  OF  THE  CORRESPONDING 

MEASUREMENTS  OF  COCKERELS 


Approximate  slaughter  weight  

2 

3 

4 

5 

Ibs. 

Ibs. 

Ibs. 

IDS. 

Age  in  days  

73 

94 

189 

219 

Live  weight  in  grams  

961 

1  342 

1  842 

2  340 

Depth  at  front  end  of  keel  

96 

98 

93 

95 

Depth  at.  rear  end  of  keel  

99 

96 

99 

107 

Length  of  keel  

97 

100 

102 

104 

Length  of  drumstick  

96 

99 

87 

86 

Length  of  shank  

94 

97 

84 

84 

Length  of  middle  toe  

90 

93 

87 

84 

Rump  to  shoulder  

97 

98 

95 

91 

Mid-circumference  

98 

97 

91 

91 

Breadth  at  hips  

96 

104 

92 

98 

The  pullets  at  any  weight  were,  in  general,  smaller  in  external 
measurement  than  the  cockerels  of  like  weight  (Table  6).  The  only 
measurement  remaining  approximately  the  same  in  the  two  sexes  is 


80 


BULLETIN  No.  278 


[June, 


the  length  of  keel.  The  leg  measurements  of  the  pullets  in  particular 
were  appreciably  smaller  than  those  of  the  cockerels,  especially  after 
the  weight  of  3  pounds  was  reached. 

A  similar  comparison  of  capons  and  cockerels  is  made  in  Table  7. 
Altho  most  of  the  measurements  on  the  capons  were  slightly  less  than 
the  corresponding  measurements  on  cockerels  of  similar  weight,  no 
very  distinct  differences  are  evident.  Castration  does  not  appreciably 
affect  the  body  conformation  of  White  Plymouth  Rock  chickens. 


TABLE  7. — AVERAGE  BODY  MEASUREMENTS  OP  WHITE  PLYMOUTH  ROCK  CAPONS  AT 

DIFFERENT  WEIGHTS,  EXPRESSED  AS  PERCENTAGES  OF  THE  CORRESPONDING 

MEASUREMENTS  OF  COCKERELS 


Approximate  slaughter  weight  

3 

4 

5 

6 

7 

IDS. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Age  in  days  

88 

170 

180 

215 

240 

Live  weight  in  grams  

1  375 

1  702 

2  285 

2  684 

3  188 

Depth  at  front  end  of  keel  

101 

98 

101 

99 

99 

Depth  at  rear  end  of  keel  

97 

96 

105 

97 

97 

Length  of  keel  

94 

95 

99 

99 

97 

Length  of  drumstick  

101 

98 

100 

101 

99 

Length  of  shank  

103 

97 

100 

99 

99 

Length  of  middle  toe  

98 

98 

97 

99 

97 

Rump  to  shoulder  

97 

100 

96 

102 

100 

Length  over  all  

97 

102 

98 

98 

98 

Mid-circumference  

100 

94 

100 

100 

105 

Breadth  at  hips  

104 

95 

96 

98 

93 

SURFACE  AREA  OF  THE  BIRDS  AT  DIFFERENT  AGES 

One  of  the  objects  of  this  investigation  was  to  determine  the  sur- 
face area  of  the  birds  at  different  ages  and  weights,  for  the  purpose  of 
deriving  a  formula  by  which  the  area  of  a  bird  may  be  computed  from 
certain  measurements  that  can  be  taken  readily  on  the  live  bird.  The 
idea  in  mind  was  to  use  such  a  formula  in  later  work  in  determining 
the  intensity  of  the  basal  heat  production  per  unit  of  body  surface. 
Therefore,  after  the  birds  were  killed  and  picked,  the  skin  was  re- 
moved and  cut  up  into  sections  that  would  flatten  out  evenly.  The 
sections  were  then  stretched  on  paper,  pinned  down,  and  outlined  in 
pencil.  It  was  very  soon  found  that  the  skins  were  quite  elastic,  so 
that  the  tension  of  the  stretched  skin  could  be  varied  considerably.  In 
all  of  this  work,  therefore,  the  skins  were  stretched  about  as  much  as 
possible,  and  in  order  to  determine  the  error  resulting  from  differences 
in  the  tension  applied,  each  skin  was  stretched  independently  by  two 
men  and  thus  outlined  twice.  The  area  of  each  outline  was  then 
measured  with  a  planimeter. 

The  average  results  of  these  determinations  are  given  in  Table  8. 
There  is  also  included,  for  each  group  of  5  birds,  the  average  percent- 


1926] 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


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82  BULLETIN  No.  278  \_June. 

age  difference  between  duplicate  determinations.  It  is  evident  that 
the  error  in  this  direct  determination  of  skin  area  is  considerable  and 
varies  widely.  It  also  appears  that,  except  for  the  4-pound  birds,  the 
skin  area  of  cockerels,  pullets,  and  capons  of  similar  weight  was  quite 
similar.  At  least  no  constant  differences  between  the  three  groups  of 
birds  are  revealed. 

The  first  attempt  to  estimate  the  skin  area  of  the  cockerels,  for 
which  the  most  complete  series  of  determinations  wras  available,  is 
shown  in  Table  9.  Since  the  Meeh  formula  is  the  simplest  formula 
relating  surface  to  weight,  and  hence  the  most  practicable  when  a 
reasonable  degree  of  accuracy  can  be  realized  by  its  use,  it  was  ap- 
plied first  to  the  nine  groups  of  cockerels.  The  average  value  for  k 
from  these  nine  average  determinations  was  9.55.  A  comparison  of  the 
actual  skin  areas  with  the  estimated  skin  areas,  using  the  formula 
S  =  9.55  W%,  is  given  in  the  upper  part  of  the  table.  The  formula 
evidently  gives  a  very  poor  determination  for  the  .5-pound  chicks,  and 
an  indifferent  determination  for  the  1-,  5-,  and  6-pound  birds. 

If  the  .5-pound  chicks  are  disregarded  in  the  determination  of  the 
Meeh  constant,  the  average  value  of  this  constant  becomes  9.85  in- 
stead of  9.55.  Using  the  latter  constant  in  estimating  the  skin  area  of 
the  last  eight  groups  of  birds,  the  values  given  in  the  lowrer  half  of 
Table  9  are  obtained.  While  the  estimated  areas  for  the  5-  and  6- 
pound  birds  are  less  in  error  than  the  estimates  by  the  other  formula, 
the.  estimate  for  the  1-pound  chicks  is  considerably  less  accurate. 
However,  the  Meeh  formula  can  be  considered  to  apply  with  consid- 
erable accuracy  to  birds  weighing  more  than  1  pound,  and  if  the  con- 
stant were  still  further  raised,  even  a  better  fit  would  be  obtained 
above  this  weight.  The  success  of  the  Meeh  formula  as  applied  to 
the  estimation  of  the  surface  area  of  White  Plymouth  Rock  chicks  is 
to  be  expected  from  the  fact  illustrated  in  Table  5  that  the  conforma- 
tion of  this  breed  of  birds  is  not  greatly  affected  by  size. 

In  attempting  to  improve  the  Meeh  formula  for  chickens,  the 
successful  experience  of  investigators,  wrorking  with  other  animals,  in 
introducing  a  linear  body  measurement  into  the  formula,  was  con- 
sidered. The  measurement  most  frequently  used  with  the  weight  in 
defining  the  conformation  of  an  animal  is  a  measurement  relating  to 
the  body  length.  Thus,  Du  Bois'  formula  for  computing  the  surface 
area  of  human  beings  introduces  the  height  measurement,  while  the 
formulas  of  Hogan  and  Skouby3  for  the  determination  of  the  surface 
area  of  cattle  and  swine  introduce  a  body  length  formula,  that  is,  the 
length  from  the  point  of  the  withers  to  the  end  of  the  ischium,  or  to 
the  root  of  the  tail.  The  corresponding  measurement  on  a  chicken 
might  be  taken  as  the  total  body  length  from  beak  to  rump.  But  in 
the  experience  of  the  authors,  this  length  is  difficult  to  take  accurately, 


1926] 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


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84  BULLETIN  No.  278  [June, 

because  the  distance  obtained  depends  so  much  on  the  tension  used  in 
stretching  out  the  bird.  An  alternative  measurement  which  could  be 
obtained  with  great  accuracy  was  the  shoulder-to-rump  measurement. 
However,  a  formula  involving  both  weight  and  rump-to-shoulder  dis- 
tance that  would  apply  satisfactorily  to  all  nine  groups  of  cockerels 
could  not  be  found,  the  error  in  estimating  the  area  of  the  .5-pound 
chicks  being  almost  as  great  as  that  resulting  from  the  application  of 
the  Meeh  formula.  If  the  .5-pound  chicks  are  disregarded,  however, 
the  following  formula  is  found  to  apply  satisfactorily  to  the  heavier 
cockerels:  S  =  5.86  W-5L-G,  in  which  S  is  the  area  in  square  centime- 
ters, W  the  body  weight  in  grams,  and  L  the  rump-to-shoulder  meas- 
urement in  centimeters. 

The  estimates  made  by  this  formula  of  the  area  of  the  remaining 
eight  groups  of  cockerels  are  given  in  the  upper  section  of  Table  10. 
While  this  formula  gives  a  better  estimate  of  surface  area  in  these 
classes  than  the  Meeh  formula,  the  estimate  for  the  1 -pound  birds  is 
still  appreciably  higher  than  the  actual  area. 

Using  the  same  formula  with  the  same  constant  in  estimating  the 
area  of  the  pullets  and  capons,  satisfactory  results  were  obtained  with 
the  exception  of  the  4-pound  birds  in  each  of  the  groups.  For  some 
reason,  at  present  unknown,  the  observed  areas  of  the  4-pound  capons, 
and  to  a  less  extent  of  the  4-pound  pullets,  were  considerably  higher 
than  the  areas  of  the  4-pound  cockerels,  and  were  so  much  greater 
than  the  observed  areas  for  the  3-pound  pullets  and  capons  that  they 
may  be  considered  as  exceptional  values,  not  representative  of  birds  of 
this  size.  Since  there  seemed  to  be  no  hope  of  devising  a  formula  that 
would  take  care  of  these  exceptional  values  any  better  than  the  one 
given  above,  no  further  attempt  was  made  to  improve  upon  it. 

In  attempting  to  see  whether  the  weight-body-length  formula 
given  above  for  White  Plymouth  Rock  chickens  would  apply  to  other 
breeds  of  chickens,  the  weight,  the  distance  from  rump  to  shoulder, 
and  the  skin  areas  of  5  Rhode  Island  Red  hens  and  of  5  Single  Comb 
White  Leghorn  hens  were  determined.  The  area  was  then  estimated 
by  means  of  the  formula  derived  from  White  Plymouth  Rock  meas- 
urements. The  results  of  this  test  are  given  in  Table  11,  from  which 
it  is  evident  that  the  areas  of  the  Rhode  Island  Red  hens  could  be 
estimated  with  considerable  accuracy  with  this  formula,  probably  just 
as  accurately  as  they  could  be  measured  directly  by  skinning  the  birds. 
For  the  White  Leghorn  hens,  however,  the  estimate  was  always  con- 
siderably in  excess  of  the  actual  area.  However,  by  reducing  the  con- 
stant from  5.86  to  5.03,  the  resulting  estimates  of  skin  area  were  sat- 
isfactory. The  conformation  of  Rhode  Island  Red  hens  is  very 
similar  to  that  of  White  Plymouth  Rock  hens,  while  the  conformation 
of  White  Leghorn  hens  is  distinctly  different. 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


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THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


87 


RELATIVE  AND  ABSOLUTE  GROWTH  OF  THE  DIFFERENT  PARTS 
OF  THE  CARCASS  AND  VISCERA 

The  growth  of  the  different  parts  of  the  carcass  and  of  the  viscera 
of  the  groups  of  cockerels,  pullets,  and  capons  is  represented  by  the 
average  values  given  in  Tables  12,  13,  and  14.  These  tables  include 
the  average  weights  for  each  group  of  5  birds.  Again  the  two  lots  of 
1-pound  birds  have  been  averaged  together,  since  the  difference  of  two 
weeks  in  their  ages  did  not  seem  to  affect  the  results  materially.*  Most 
of  the  viscera  and  the  different  parts  of  the  carcass  increase  continu- 
ously with  increasing  body  weight.  For  cockerels  the  rapid  increase  in 
size  of  the  testicles  at  about  the  6-pound  weight  clearly  indicates  the 
time  of  sexual  maturity.  The  digestive  organs  are  somewhat  excep- 
tional in  their  growth,  since  they  reach  their  maximum  size  before  the 
bird  has  obtained  its  complete  growth.  This  is  true  of  all  three  groups 
of  birds.  The  weights  of  the  gizzard  and  of  the  intestinal  tract  ex- 
clusive of  the  gizzard  reach  their  maximum  when  the  weight  of  the 
bird  is  5  or  6  pounds.  The  weights  of  the  spleen  and  liver  increase 
but  little  after  this  body  weight  is  reached.  This  attainment  of  max- 
imum growth  of  the  digestive  tract  at  a  time  when  the  body  has  not 
ceased  growing  is  also  shown  by  the  data  in  Table  15,  relative  to  the 
length  of  the  intestinal  tract.  The  maximum  length  of  intestinal 
tract  seems  to  be  reached  at  a  weight  of  5  pounds. 

Data  on  the  growth  of  the  different  parts  of  the  carcass  and  the 
different  visceral  organs,  which  show  for  each  weight  group  the  per- 
centages of  the  empty  weight  of  the  bird  reached  by  each  organ  and 
each  part  of  the  carcass,  are  presented  in  Tables  16,  17,  and  18.  The 
empty  weight  was  obtained  by  deducting  from  the  average  live  weight 


*The  average  weights  of  the  different  organs  and  parts  of  carcass  for  the  two 
groups  of  birds  of  approximately  the  same  weight  (1  pound)  but  at  different 
ages,  were  as  follows,  all  weights  being  given  in  grams: 


Age 
days 

Body 
weight 

Blood 

Feathers 

Head 

Shanks 
+  feet 

Heart 

Liver 

Kidneys 

Pan- 
creas 

Spleen 

43... 
57  

446 

452 

21 
19 

18 
16 

19 
20 

23 
23 

3.0 
2.9 

16 
15 

4.5 

1.9 
1.7 

0.8 
1.1 

^AgC 

days 

Viscera  and  offal  (cont'd) 

Dressed  carcass 

Lungs 

Testi- 
cles 

Intestinal 
tract 
minus 
gizzard 

Gizzard 

Contents 
of  intes- 
inal  tract 

Neck 

Skin 

Legs 
above 
hock 

Wings 

Torso 

43... 
57  

2.5 
2.7 

0.2 
0.1 

46 
39 

16 
19 

30 
23 

15 
16 

32 
33 

74 
79 

27 
27 

95 
95 

The  total  bone  on  the  dressed  carcass  weighed  70  and  75  grams  respectively 
for  the  two  groups  of  birds,  while  the  total  flesh  on  the  dressed  carcass  weighed 
131  and  138  grams  respectively. 


88 


BULLETIN  No.  278 


[June, 


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DRESSED  CARCAS 
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THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


of  each  group  of  birds  the  average  weight  of  the  contents  of  the  in- 
testinal tract,  including  the  gizzard.  For  convenience  of  study,  the 
organs  and  different  parts  of  the  carcass  have  been  arranged  into  three 
main  groups:  first,  the  offal,  which  in  this  tabulation,  however,  does 
not  include  the  inedible  viscera;  second,  the  visceral  organs;  and 
third,  the  different  parts  of  the  dressed  carcass.  It  is  interesting  to 
note  that  the  offal  parts  of  the  carcass  constitute  a  fairly  constant  per- 
centage of  the  empty  live  weight  of  the  birds  at  all  weights,  namely, 
very  close  to  19  percent.  At  the  heavier  weights  there  is  a  slight 

TABLE  13. — AVERAGE  WEIGHTS  OF  PARTS  OF  CARCASS  OF  WHITE  PLYMOUTH  ROCK 
PULLETS  KILLED  AT  DIFFERENT  WEIGHTS:   EACH  FIGURE  Is  AN  AVERAGE 

OF  FIVE  BIRDS 
(All  weights  are  in  grams) 


Approximate  slaughter  weight  

2 

3 

4 

5 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Age  in  days  

73 

94 

189 

219 

Live  weight  in  grams  

961 

1  342 

1  842 

2  340 

VISCERA  AND  OFFAL 
Blood  

34 

41 

59 

79 

Feathers  

66 

108 

152 

168 

Head  

28 

37 

49 

53 

Shanks  and  feet  ...        .  .        .    .        

46 

61 

66 

80 

Heart  

4.5 

5.4 

8.5 

10.1 

Liver  

23 

28 

31 

43 

Kidneys  

6.2 

8.1 

9.8 

13.9 

Pancreas  

-    2.8 

2  9 

4.3 

4.9 

Spleen  

2.4 

3.0 

3.3 

4.8 

Lungs  

4  2 

6  6 

8  0 

8.9 

Intestinal  tract  exclusive  of  gizzard  

65 

83 

108 

128 

Gizzard  

39 

47 

60 

65 

Contents  of  digestive  tract  

46 

49 

55 

95 

DRESSED  CARCASS 
Neck  

35 

45 

52 

61 

Skin  

73 

103 

164 

225 

Legs  above  hock  

167 

258 

344 

428 

Wings  i  

57 

82 

97 

122 

Torso  

220 

345 

524 

681 

Total  bone  in  carcass  (except  head,  shanks,  and 
feet)  

161 

224 

268 

332 

Total  flesh  and  fat  in  carcass  (except  head,  shanks, 
and  feet)  

311 

497 

733 

941 

tendency  for  this  percentage  to  decrease.  This  constancy  in  percent- 
age weight  is  particularly  apparent  for  the  blood  weights.  Blood  ap- 
parently constitutes  a  consistently  higher  percentage  of  the  empty 
weight  for  the  cockerels  than  for  either  capons  or  pullets,  the  capons 
ranking  next  to  the  cockerels  in  this  respect. 

Following  an  initial  increase  from  the  .5-pound  to  1-pound  chicks, 
the  percentage  weight  of  the  total  viscera  shows  a  continuous  decrease 


90 


BULLETIN  No.  27S 


[June, 


TABLE  14. — AVERAGE  WEIGHTS  OF  PARTS  OF  CARCASS  OF  WHITE  PLYMOUTH  ROCK 
CAPONS  KILLED  AT  DIFFERENT  WEIGHTS:    EACH  FIGURE  Is  AN  AVERAGE 

OF  FIVE  BIRDS 
(All  weights  are  in  grams) 


Approximate  slaughter  weight       

3     • 

4 

5 

6 

7 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Age  in  days  

88 

170 

180 

215 

240 

Live  weight  in  grams  

1  375 

1  702 

2  285 

2  684 

3  188 

VISCERA  AND  OFFAL 
Blood  

54 

67 

96 

91 

113 

Feathers  

86 

141 

178 

201 

222 

Head  

40 

51 

57 

60 

70 

Shanks  and  feet  

77 

88 

111 

129 

124 

Heart  

6.1 

6.9 

9  1 

11  0 

13  6 

Liver  

32 

36 

49 

51 

70 

Kidneys  

8.4 

10.2 

12.1 

14.1 

16.2 

Pancreas  .            .    . 

2  7 

3  7 

4  9 

5  6 

5  4 

Spleen  

2.8 

4.1 

4.6 

5  9 

6  4 

Lungs  

6  8 

9  8 

11  1 

12  8 

12  9 

Intestinal  tract  exclusive  of  gizzard  .... 
Gizzard  

84 
47 

93 

57 

133 
61 

158 
74 

152 
79 

Contents  of  intestinal  tract  

60 

46 

60 

85 

95 

DRESSED  CARCASS 
Neck  

48 

58 

69 

82 

89 

Skin  

99 

136 

191 

228 

272 

Legs  above  hock  

267 

346 

475 

528 

610 

Wings  

86 

105 

131 

148 

183 

Torso  

331 

405 

566 

733 

969 

Total   bone   in    carcass    (except   head, 
shanks,  and  feet)  

238 

319 

391 

441 

497 

Total  flesh  and  fat  in  carcass  (except 
head,  shanks,  and  feet)  

485 

559 

815 

1  019 

1  360 

TABLE  15. — LENGTH  OF  INTESTINAL  TRACT  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 
KILLED  AT  DIFFERENT  WEIGHTS:    EACH  FIGURE  Is  AN  AVERAGE  OF 

FIVE  BIRDS 
(All  measurements  are  in  centimeters) 


Approximate  slaughter 
weight  

0.5 

Ib. 

1 

Ib. 

1.5 

Ibs. 

2 
Ibs. 

3 
Ibs. 

4 
Ibs. 

5 
Ibs. 

6 
Ibs. 

7 
Ibs. 

COCKERELS 
Intestines  

102 

134 

142 

149 

166 

176 

189 

184 

174 

Ceca  (total)  

21 

26 

32 

34 

35 

42 

49 

45 

45 

PULLETS 
Intestines  

152 

151 

165 

176 

Ceca  (total)  

42 

35 

40 

48 

CAPONS 
Intestines  

162 

165 

190 

193 

198 

Ceca  (total)  

40 

38 

61 

50 

48 

THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


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i 

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Approximate 

Age  in  days 
Percentage  ' 
Empty  weig 

m            oj  {jj 
O 

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lllllijlll 

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92 


BULLETIN  No.  278 


[June, 


with  increasing  weight  of  the  birds,  this  being  true  for  all  three  groups 
of  birds.  Jackson1  and  Donaldson5  have  shown  that  the  relative 
weight  of  the  viscera  decreases  with  increasing  body  weight  in  the  case 
of  the  albino  rat,  man,  and  other  mammals.  This  relative  decrease  is 
shown  for  all  organs  listed  except  the  testicles,  and  is  particularly  pro- 
nounced for  the  digestive  tract.  The  decrease  is  not  so  marked  for 
the  heart,  kidneys,  and  lungs. 

Donaldson6,  has  shown  that  the  musculature  contributes  most  to 
the  increasing  weight  of  growing  mammals.  That  the  same  is  true  for 
growing  fowls  is  indicated  by  the  tables  under  discussion.  The  per- 
centage weight  of  the  total  dressed  carcass  increases  slightly  but  con- 

TABLE  17. — AVERAGE  WEIGHTS  OF  PARTS  OF  CARCASS  OF  WHITE  PLYMOUTH  ROCK 

PULLETS  KILLED  AT  DIFFERENT  WEIGHTS,  EXPRESSED  IN  PERCENTAGE 

OF  THE  EMPTY  WEIGHT 


Approximate  slaughter  weight  

2 

3 

4 

5 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Age  in  days  

73 

94 

189 

219 

Percentage  "fill"  

4.8 

3.7 

2.6 

3.7 

Empty  weight  in  grams  

915 

1  293 

1  787 

2  245 

OFFAL 
Feathers  

percl. 
7.2 

percl. 
8.4 

percl. 
8.5 

perct. 
7.5 

Blood  

3.7 

3.2 

3.3 

3.5 

Head  

3.1 

2.9 

2.7 

2.4 

Shanks  and  feet  

5.0 

4.7 

3.7 

3.6 

Tota>  offal  

19.0 

19.1 

18.2 

16.9 

VISCERA 
Heart  

0.49 

0.42 

0.48 

0.45 

Liver  

2.5 

2.2 

1.7 

1.9 

Kidneys  

0.68 

0.63 

0.55 

0.62 

Pancreas  

0.31 

0.22 

0.24 

0.22 

Spleen  

0.26 

0.23 

0.18 

0.21 

Lungs  ;  '  

0.46 

0.51 

0.45 

0.40 

Digestive  tract  

11.4 

10.1 

9.4 

8.6 

Total  viscera  

16.1 

14.2 

12.9 

12.4 

DRESSED  CARCASS 
Skin  

8.0 

8.0 

9.2 

10.0 

Neck  .         

3.8 

3.5 

2.9 

2.7 

Legs  above  hock  

18.3 

20.0 

19.3 

19.0 

Wings  

6.2 

6.3 

5.4 

5.4 

Torso  

24.0 

26.7 

29.3 

30.2 

Total  dressed  carcass  

60.3 

64.4 

66.1 

67.3 

Total  bone  in  dressed  carcass  

17.6 

17.3 

15.0 

14.7 

Total  flesh  and  fat  in  dressed  carcass  

34.0 

38.4 

41.0 

41.8 

Total  flesh,  fat,  and  edible  viscera3  

41.9 

45.3 

47.0 

47.6 

alncluding  heart,  liver,  gizzard,  and  kidneys. 

tinuously  with  increasing  weight  of  body.    This  increase  is  particularly 
marked  for  the  "torso. "a    For  the  cockerels  the  relative  weight  of  the 

'"Torso"  in  this  connection  refers  to  the  carcass  of  the  bird  minus  the  skin, 
neck,  legs,  and  wings. 


1926'} 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


93 


legs  above  hock  also  increases  steadily  with  increasing  body  weight, 
while  for  the  pullets  and  capons  the  percentage  weight  of  the  legs 
above  hock  is  practically  constant  for  all  body  weights.  The  percent- 
age weight  of  the  skin  also  increases,  while  that  for  the  wings  decreases 
for  all  three  groups  of  birds. 

That  the  relative  increase  in  dressed  carcass  relates  to  the  muscu- 
lature and  not  to  the  bones  is  shown  by  the  percentages  at  the  bottom 

TABLE  18. — AVERAGE  WEIGHTS  OF  PARTS  OF  CARCASS  OF  WHITE  PLYMOUTH  ROCK 

CAPONS  KILLED  AT  DIFFERENT  WEIGHTS,   EXPRESSED  IN  PERCENTAGE 

OF  THE  EMPTY  WEIGHT 


Approximate  slaughter  weight  

3 

4 

5 

6 

7 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Age  in  days  

88 

170 

180 

215 

240 

Percentage  "fill"  

4  4 

2  7 

2  6 

3  5 

3  0 

Empty  weight  in  grams  

1  315 

1  656 

2  225 

2  599 

3  093 

OFFAL 
Feathers  

perd. 
6.5 

perct. 
8.5 

perct. 
8  0 

perct. 

7  8 

perct. 
7  2 

Blood  

4  1 

4  0 

4  3 

3  5 

3  7 

Head  

3.0 

3.1 

2.6 

2.3 

2.3 

Shanks  and  feet  

5.8 

5.4 

5.0 

5.0 

4  0 

Total  offal  

19.5 

21.0 

19.9 

18.6 

17  1 

VISCERA 
Heart  

0  46 

0  42 

0  41 

0  42 

0  44 

Liver  

2.4 

2.2 

2.2 

1.9 

2.3 

Kidneys                      .  . 

0  64 

0  62 

0  54 

0  54 

0  52 

Pancreas  

0.21 

0.22 

0.22 

0.22 

0  17 

Spleen  

0.21 

0.25 

0.21 

0  23 

0  21 

Lungs.  . 

0  52 

0  59 

0.50 

0  49 

0  42 

Digestive  tract  

10  0 

9  1 

8  7 

9  0 

7  5 

Total  viscera  

14  4 

13  3 

12  7 

12  7 

11  5 

DRESSED  CARCASS 
Skin  

7.5 

8.2 

8.6 

8.8 

8.8 

Neck  

3.6 

3.5 

3.1 

3.2 

2.9 

Legs  above  hock  

20  3 

20.9 

21.3 

20.4 

19  7 

Wings  

6  5 

6  3 

5.9 

5.7 

5  9 

Torso  

25  2 

24  5 

25.4 

28  3 

31  3 

Total  dressed  carcass  

63.2 

64.6 

64.4 

66.4 

68.6 

Total  bone  in  dressed  carcass  

18  1 

19  3 

17  6 

17.0 

16  1 

Total  flesh  and  fat  in  dressed  carcass.  .  .  . 
Total  flesh,  fat,  and  edible  viscera*  

36.9 
44,0 

33.8 
40.4 

36.6 
42.4 

39.3 
45.0 

44.0 
49.7 

alncluding  heart,  liver,  gizzard,  and  kidneys. 

of  Tables  16,  17,  and  18.  For  all  three  groups  of  birds  the  percentage 
weight  of  the  bone  in  the  dressed  carcass  decreases  with  increasing 
body  weight,  while  the  percentage  weight  of  the  total  flesh  and  fat 
increases.  The  relative  weight  of  total  flesh,  fat,  and  edible  viscera 
(heart,  liver,  gizzard,  and  kidneys)  also  increases  with  increasing 
weight  of  body. 


94 


BULLETIN  No.  278 


[June, 


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1 

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T3  c  C  0> 

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03    M 

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03    > 
T3  F 

.    .    .  « 

j    !g 

£         ^  ° 
<  «>2  «  J-  "o 

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lisillife  Ijiliii 

g  ffl  J  S  PH  CB1*-^  Q  H       a^^i^^hH 

Total  bone  in  dre 
Total  flesh  and  fa 
(exclusive  of 
Total  flesh,  fat,  a 

i 
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Is 

2  g 
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wh-  1 


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1926'} 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


95 


The  increase  in  weight  of  the  different  parts  of  the  carcass  and 
the  different  visceral  organs  relative  to  the  weights  in  the  .5-pound 
chicks  is  shown  for  the  cockerels  in  Table  19.  In  this  table  the  weights 
for  the  different  parts  of  the  .5-pound  chicks  are  taken  as  100,  and  the 
weights  in  the  groups  of  increasing  weight  are  expressed  in  percentage 
of  the  corresponding  weights  in  the  .5-pound  group.  A  study  of  Table 
19  gives  much  the  same  information  as  the  study  just  concluded.  Thus, 

TABLE  20. — AVERAGE  WEIGHTS  OF  PARTS  OF  CARCASS  OF  WHITE  PLYMOUTH  ROCK 
PULLETS  KILLED  AT  DIFFERENT  WEIGHTS,  EXPRESSED  IN  PERCENTAGE  OF 
THE  CORRESPONDING  WEIGHTS  OF  THE  COCKERELS 


Approximate  slaughter  weight  

2 

3 

4 

5 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Age  in  days  

73 

94 

189 

219 

Empty  weight  in  grams  

94 

99 

104 

105 

OFFAL 
Feathers  

perci. 
143 

perct. 
130 

perct. 
114 

perct. 
96 

Blood  

74 

77 

82 

83 

Head  

85 

86 

91 

87 

Shanks  and  feet  

82 

74 

69 

71 

Total  off  al  

96 

95 

92 

86 

VISCERA 
Heart  

98 

96 

116 

109 

Liver  

105 

93 

86 

96 

Kidneys  

100 

104 

114 

122 

Pancreas  

97 

100 

116 

100 

Spleen  

126 

111 

114 

120 

Lungs  

100 

99 

88 

75 

Gizzard  

103 

100 

109 

92 

Digestive  tract,  total  

99 

100 

113 

101 

Total  viscera  

94 

99 

106 

100 

DRESSED  CARCASS 
Skin  

103 

113 

129 

128 

Neck  

92 

94 

83 

84 

Legs  above  hock  

86 

92 

90 

90 

Wings  

92 

94 

86 

96 

Torso  

103 

113 

123 

127 

Total  dressed  carcass  

95 

103 

106 

109 

Total  bone  in  dressed  carcass  

87 

92 

81 

83 

Total  flesh  and  fat  in  dressed  carcass  

96 

105 

117 

118 

Total  flesh,  fat,  and  edible  viscera  

97 

104 

115 

115 

while  the  empty  weight  of  the  birds  increases  at  a  body  weight  of  7 
pounds  to  a  value  14.73  times  the  empty  weight  of  .5-pound  birds,  the 
total  offal  increases  13.67  times,  the  total  viscera  6.77  times,  and  the 
total  dressed  carcass  18.88  times.  The  bones  in  the  carcass  increase  in 
weight  13.08  times,  while  the  total  flesh  and  fat  increase  27.09  times. 
A  comparison  between  the  pullets,  capons,  and  cockerels  relative 
to  the  weights  of  the  different  parts  of  the  carcass  and  the  different 


96 


BULLETIN  No.  278 


[June, 


visceral  organs  at  different  body  weights,  is  afforded  by  the  data  given 
in  Tables  20  and  21.  In  these  tables  the  weights  of  the  different  parts 
and  organs  for  each  group  of  pullets  and  capons  are  expressed  as  per- 
centages of  the  corresponding  weights  for  the  cockerels. 


TABLE  21. — AVERAGE  WEIGHT  OF  PARTS  OF  CARCASS  OF  WHITE  PLYMOUTH  ROCK 

CAPONS  KILLED  AT  DIFFERENT  WEIGHTS,  EXPRESSED  IN  PERCENTAGE  OF 

THE  CORRESPONDING  WEIGHTS  FOR  THE  COCKERELS 


Approximate  slaughter  weight  

3 

4 

5 

6 

7 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Age  in  days  

88 

170 

180 

215 

240 

Empty  weight  in  grams  

101 

96 

103 

103 

97 

OFFAL 
Feathers  

perct. 
104 

perct. 
105 

perct. 
102 

perct. 
99 

perct. 
121 

Blood  

102 

93 

101 

86 

75 

Head  

93 

94 

93 

84 

69 

Shanks  and  feet  

94 

93 

98 

113 

95 

Total  offal  

98 

98 

100 

97 

93 

VISCERA 
Heart  

109 

94 

98 

98 

65 

Liver  

107 

100 

109 

100 

167 

Kidneys  

108 

119 

106 

108 

131 

Pancreas  

93 

100 

100 

127 

100 

Spleen  .... 

104 

141 

115 

147 

183 

Lungs  

101 

108 

93 

113 

94 

Gizzard  

100 

104 

86 

109 

120 

Digestive  tract  

101 

101 

102 

116 

125 

Total  viscera  

102 

101 

101 

109 

113 

DRESSED  CARCASS 
Skin  

109 

107 

109 

120 

100 

Neck  .  .  . 

100 

92 

95 

96 

83 

Legs  above  hock  

95 

91 

100 

95 

77 

Wings  

99 

93 

103 

99 

100 

Torso  

109 

95 

105 

111 

113 

Total  dressed  carcass  

102 

96 

103 

105 

96 

Total  bone  in  dressed  carcass  

98 

97 

97 

106 

97 

Total  flesh  and  fat  in  dressed  carcass.  .  .  . 
Total  flesh,  fat,  and  edible  viscera  

103 
103 

89 
91 

102 
101 

101 
101 

93 
96 

The  weights  of  the  total  offal  are  consistently  less  for  the  pullets 
than  for  the  cockerels  (Table  20) .  This  is  true  of  each  division  of  the 
offal  except  the  feathers.  The  weights  of  feathers  for  the  pullets  were 
generally  greater  than  those  for  the  cockerels,  the  differences  decreasing 
with  advancing  body  weight.  The  total  weights  of  viscera  did  not 
differ  greatly  for  cockerels  and  pullets,  this  being  particularly  true  of 
the  pancreas,  liver,  and  the  digestive  tract.  When  the  pullets  reached 
a  weight  of  2  pounds,  their  lungs  weighed  the  same  as  the  lungs  of 
the  cockerels,  but  with  increasing  body  weight  the  lungs  of  the  cock- 
erels weighed  increasingly  more  than  those  of  the  pullets.  Just  the 


1926] 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


97 


reverse  is  true  with  the  kidneys,  which  were  heavier  in  the  pullets  than 
in  the  cockerels,  the  differences  increasing  with  increasing  body 
weight.  The  weights  of  spleen  were  consistently  heavier  for  the  pul- 
lets than  for  the  cockerels.  The  dressed  carcass  in  the  pullets  was  al- 
ways slightly  heavier  than  in  the  cockerels  for  body  weights  of  3 
pounds  or  more,  this  being  entirely  referable  to  the  weights  of  the 
skin  and  of  torso.  For  the  other  parts  of  the  carcass,  particularly  for 
the  neck,  the  cockerel  weights  are  consistently  greater  than  the  pullet 
weights.  The  weights  of  bone  in  the  dressed  carcass  were  always 

TABLE  22. — DIFFERENCES  BETWEEN  COCKERELS  AND  CAPONS  WEIGHING  SEVEN 

POUNDS  IN  THE  WEIGHTS  OF  CERTAIN  VISCERAL  ORGANS 

(All  weights  are  in  grams) 


Kind  and 

No.  of 

Heart 

Liver8 

Spleen 

Gizzard 

Intestines 

Kidneys 

bird 

COCKERELS 

2115  

26.0 

45 

3.4 

66 

69 

13.0 

2174  

20.9 

42 

4.1 

60 

75 

12.1 

2713  

21.4 

48 

4.0 

70 

91 

14.8 

2825  

17.3 

32 

3.0 

62 

63 

11.0 

2111  

19.9 

41 

3.1 

72 

59 

11.3 

CAPONS 

2755  

13.5 

77 

8  1 

74 

101 

13  8 

2152  

15  7 

66 

7  0 

78 

136 

16  8 

2614  

10  9 

59 

5  0 

78 

96 

18  3 

2482  

12.7 

73 

7.1 

67 

94 

13.6 

2761  

15.0 

74 

4.7 

98 

101 

18.5 

"The  weight  of  gall  bladder  is  included  in  the  weight  of  liver. 

greater  at  the  same  body  weight  for  cockerels  than  for  pullets,  while 
the  total  flesh  and  fat  were  always  greater  for  the  pullets  at  body 
weights  of  3  pounds  or  more. 

The  differences  between  cockerels  and  capons  are  not  so  consis- 
tent as  those  between  cockerels  and  pullets.  The  weights  of  offal  were 
much  the  same  for  capons  and  cockerels  at  all  ages,  except  for  the 
weights  of  head  and  of  blood,  which  at  body  weights  of  more  than  5 
pounds  were  greater  in  the  cockerels  than  in  the  capons,  the  difference 
increasing  with  increasing  body  weight.  The  weights  of  viscera  also 
were  much  the  same  for  cockerels  and  capons  for  similar  body  weights, 
except  for  the  7-pound  weight,  at  which  the  total  viscera  for  the  capons 
weighed  13  percent  more  than  for  the  cockerels. 

Some  interesting  differences  between  the  two  groups  appear  at  the 
7-pound  weight  with  reference  to  the  heart,  liver,  spleen,  kidney,  and 
digestive  tract.  While  the  marked  differences  in  the  weights  of  heart, 
kidney,  and  liver  were  only  evident  at  the  7-pound  weight,  the  differ- 
ences in  the  weights  of  spleen  and  digestive  tract  were  also  evident  at 
smaller  weights.  For  the  spleen,  in  fact,  the  capons  showed  consist- 


98 


BULLETIN  No.  278 


[June, 


ently  greater  weights  than  the  cockerels,  from  body  weights  of  3  to 
7  pounds  inclusive.  To  illustrate  the  great  significance  of  these  dif- 
ferences in  the  two  groups  of  birds  at  7  pounds  body  weight,  Table  22, 
giving  the  individual  weights  for  all  ten  birds,  is  presented. 

Altho  considerable  variation  is  evident  among  the  individual  birds 
in  each  group  with  respect  to  the  weights  of  these  visceral  organs,  the 
differences  between  cockerels  and  capons  are  distinct.  For  example, 
in  the  case  of  the  heart  all  of  the  5  cockerels  showed  larger  weights 
than  any  of  the  5  capons,  while  in  the  case  of  the  liver,  spleen,  and 


TABLE  23. — CHEMICAL  COMPOSITION  OF  THE  BONE  SAMPLES 


Kind  of 
bird 
and  weight 

Dry 

substance 

Crude 
protein 
(Nx  6.0) 

Ash 

Ether 
extract 

Unac- 
counted 
for 

Gross 
energy 
per  gram 

COCKERELS 
Ibs. 
0.5  

perct. 
39.97 

perct. 
19.68 

perct. 
8.81 

perct  . 
4  57 

perct. 
6.91 

small  cals. 
1  703 

1  

41.46 

17  40 

11.30 

9  86 

2.90 

1  978 

1  

39.36 

18.72 

11  23 

6  87 

2.54 

1  572 

1.5  

42.42 

19.20 

12.52 

8.86 

1.84 

1  810 

2  

44.40 

17.76 

10.34 

14  75 

1.55 

2  243 

3  

45.00 

18.42 

11.19 

11  70 

3.69 

2  046 

4  

45.26 

19.86 

12.56 

12  20 

0.64 

2  194 

5  

47.61 

18.54 

14.44 

13.30 

1.33 

2  273 

6  

51.37 

18.84 

16.51 

14  47 

1.55 

2  459 

7  

50.77 

20.16 

15.73 

12  26 

2.62 

2  317 

PULLETS 
Ibs.   , 
2..Y.  

45.40 

18  18 

11  35 

13  57 

2.30 

2  145 

3  

44.35 

18.00 

10.07 

13.57 

2.71 

2  185 

4  

51.86 

17.76 

12.70 

18.30 

3.10 

2  505 

5  

54.87 

18.78 

14.30 

20  00 

1.79 

2  955 

CAPONS 
Ibs. 
3  

44  40 

18  30 

10  84 

13  40 

1.86 

2  223 

4  

46.75 

18.24 

11.82 

13.54 

3.15 

2  491 

5  

48.12 

18.72 

11.57 

16.15 

1.68 

2  628 

6  

50.76 

18.84 

14  65 

15  33 

1.94 

2  597 

7  

52.95 

17.34 

11.86 

21.62 

2.07 

2  919 

intestines,  all  the  capons  showed  larger  weights  than  any  of  the  cock- 
erels. For  the  gizzard  and  kidney  there  is  a  slight  overlapping  by  the 
two  groups,  but  nevertheless  the  differences  appear  to  be  highly  sig- 
nificant. Apparently  castration  has  profoundly  affected  the  growth 
of  these  visceral  organs,  either  directly  or  indirectly. 

These  differences  in  organ  weights  between  capons  and  cockerels, 
so  far  as  they  relate  to  the  heart,  spleen,  and  kidneys,  are  in  agree- 
ment with  results  reported  by  Marrassini  and  Luciani.7  These  authors 
explain  the  hypertrophy  of  the  spleen  in  castrated  birds  as  a  conse- 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


99 


quence  of  the  peritoneal  hemorrhages  often  resulting  from  the  removal 
of  the  testicles  in  fowls.  This  explanation  is  hardly  consistent,  how- 
ever, with  the  progressive  divergence  in  spleen  weights  among  cock- 
erels and  capons  of  increasing  weight.  The  difference  in  heart  weight 
between  castrated  and  uncastrated  male  birds  may  be  reasonably  ex- 
plained as  the  result  of  a  greater  muscular  activity  of  the  cockerels. 
Hatai8  has  shown  that  among  groups  of  rats  receiving  different 


TABLE  24. — CHEMICAL  COMPOSITION  OF  THE  SAMPLES  OF  FLESH 
AND  EDIBLE  VISCERA 


Kind  of 
bird 
and  weight 

Dry 

substance 

Crude 
protein 
(N  x  6.0) 

Crude 
fat 

Ash 

Unac- 
counted 
for 

Gross 
energy 
per  gram 

COCKERELS 
Ibs. 
0.5  

perct. 
30  07 

perct. 
20  88 

perct. 
4  38 

perct. 
1  44 

perct. 
3  37 

small  cals. 
1  526 

1  

25.40 

19.56 

3.95 

1.27 

0  62 

1  461 

1  

24.87 

19.62 

3.55 

1.31 

0  39 

1  281 

1.5  

28.63 

20.04 

6  54 

1  27 

0  78 

1  540 

2  

27  20 

18  84 

6  16 

1  07 

1  13 

1  597 

3  

28.51 

20.10 

4.39 

1.13 

2.89 

1  571 

4  

29.49 

21.00 

3.92 

1.02 

3  55 

1  460 

5  

28.49 

19.74 

5  54 

1  29 

1  92 

1  65  la 

6  

28  51 

20  22 

5  40 

1  72 

1  17 

1  714 

7  

28  08 

21  00 

4  46 

1  40 

1  22 

1  606 

PULLETS 
Ibs. 
2  

26  70 

19.02 

6  00 

1  06 

0  62 

1  515 

3  

34  09 

18  90 

9  75 

1  20 

4  24 

1  860 

4  

30  79 

18  54 

11  22 

1  01 

0  02 

2  262 

5  

33.67 

20.22 

12.62 

1.35 

-0  52 

2  356 

CAPONS 
Ibs. 
3  

28  20 

19  74 

5  99 

1  27 

1  20 

1  628 

4  

29  25 

19  26 

7  16 

1  11 

1  72 

1  787 

5  

33  10 

19  38 

8  61 

1  17 

3  94 

1  893 

6. 

31  43 

18  84 

10  29 

0  98 

1  32 

2  049 

7  

36.97 

18.00 

16.84 

0.94 

1.19 

2  543 

"Calculated  by  using  factors  5.7  calories  per  gram  of  protein  and  9.5  calories  per 
gram  of  fat. 

amounts  of  exercise,  the  weights  of  the  heart  observed  were  positively 
correlated  with  the  exercise  records,  while  Hoskins9  and  Richter10  have 
shown,  with  the  same  species  of  animal,  that  castration  markedly  low- 
ers spontaneous  activity. 

No  clear  differences  exist  between  cockerels  and  capons  with  ref- 
erence to  the  dressed  carcass  and  its  dissected  parts,  except  possibly 
with  respect  to  the  neck  and  the  legs  above  hock,  the  weights  of  which 
were,  in  general,  less  for  the  capons  than  for  the  cockerels,  especially 
at  the  7-pound  weight.  Also,  no  consistent  differences  can  be  made 


100 


BULLETIN  No.  278 


[June, 


out  between  cockerels  and  capons  in  the  weights  of  total  bone  or  of 
total  flesh  and  fat  in  the  dressed  carcass. 

CHEMICAL  COMPOSITION  OF  THE  BIRDS  AT  DIFFERENT  WEIGHTS 

Each  group  of  5  birds  was  analyzed  in  three  composite  samples: 

first,  the  total  bone  of  the  dressed  carcass;  second,  the  flesh  and  fat  of 

the  dressed  carcass  plus  the  heart,  liver,  and  gizzard;  and  third,  the 

offal  sample,  including  the  blood,  feathers,  head,  shanks  and  feet,  gall 

TABLE  25. — CHEMICAL  COMPOSITION  OF  THE  SAMPLES  OP  OFFAL 


Kind  of 
bird 
and  weight 

Dry 

substance 

Crude 
protein 
(Nx  6.0) 

Ash 

Ether 
extract 

Unac- 
counted 
for 

Gross 
energy 
per  gram 

COCKERELS 
Ibs. 
0.5  

perct. 
34.30 

perct. 
22.25 

perct. 
2.56 

perct. 
6.63 

perct. 
2  86 

small  cols. 
1  762 

1  

29.74 

21.12 

2.36 

7.67 

-1.41 

1  825 

1  

29.73 

20.20 

2.42 

5.33 

1.78 

1  601 

1.5  

33.86 

21.68 

2.37 

9.36 

0.45 

1  976 

2  

36.21 

21.04 

2.39 

9.88 

2  90 

2  092 

3..  

37.64 

24.72 

2.31 

9.72 

0  89 

2  332b 

4  

36.78 

24.15 

1.98 

8.77 

1.88 

2  289 

5  

41.54 

25.62 

2.01 

11.13 

2.78 

2  137 

6  

53.34 

34.02 

4.13 

13.12 

2  07 

2  774 

7  

51.69 

26.70 

2.65 

19.89 

2  45 

3  255 

PULLETS 
Ibs. 
2  

40.08 

24.16 

2.49 

11.86 

1.57 

2  094 

3  

37.86a 

24  22a 

2.59a 

10.35a 

0.70 

2  364b 

£:H  

49.94 
51.86 

25.83 
27.71 

1.89 
1.82 

19.14 
23  07 

3.08 
—  0  74 

2  758 
3  516 

CAPONS 
Ibs. 
3  

38.08 

23.72 

2.60 

10.98 

0.78 

2  280 

4  

40.65 

24.12 

2.02 

12.12 

2  39 

2  736 

5  

42.18 

22.29 

1.85 

14.86 

3  18 

2  803 

6  

54.18 

29.45 

2.34 

18.99 

3  40 

3  120 

7  

51.37 

25.85 

2.22 

20.87 

2.43 

3  396 

aChemical  composition  calculated  from  average  composition  of  offal  from 
3-pound  capons  and  cockerels. 

bCalculated  by  using  factors  5.7  calories  per  gram  of  protein  and  9.5  calories  per 
gram  of  fat. 

bladder,  and  the  viscera  not  included  in  the  second  sample.  These 
samples  were  all  ground  in  a  fresh  condition  and  submitted  to  routine 
analysis.  The  percentage  of  dry  substance  in  each  sample  was  cor- 
rected so  far  as  possible  for  moisture  losses  during  dissection,  weigh- 
ing, and  grinding  of  the  material.  The  gross  energy  of  each  sample 
was  also  directly  determined  in  the  bomb  calorimeter.  The  results  of 
these  analyses  and  energy  determinations  are  included  in  Tables  23, 
24,  and  25.  Altho  the  percentage  composition  of  these  samples 


1926} 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


101 


shows  a  good  deal  of  irregularity  in  comparing  birds  of  different  weight, 
there  is  a  fairly  general  tendency  for  the  dry  substance  to  increase  at 
the  heavier  weights,  and  for  the  ether  extract  to  increase  in  the  samples 
for  the  pullets  and  capons.  No  consistent  increase  in  the  ether  ex- 
tract of  the  cockerel  samples  was  manifested  after  a  weight  of  2 

TABLE  26. — PERCENTAGE  COMPOSITION  OP  LIVE  BIRDS 


Kind  of  bird 
and  weight 

Age  at 
slaughter 

Dry  sub- 
stance 

Crude 
protein 

(Nx6.0) 

Crude 
fat 

Ash 

Unac- 
counted 
for 

Gross 
energy 
per  gram 

CHICKS 
gms. 
37.5  

days 
1.5 

perct. 
24.89 

perct. 
16.18 

perct. 
5.60 

perct. 
1.83 

perct. 
1.28 

small 
cals. 

1  476 

COCKERELS 
Ibs. 
0.5  

29 

27.84 

17.46 

4.40 

2  82 

3.16 

1  366 

1  

43 

26.96 

17  81 

5  88 

3  13 

0  14 

1  499 

1  

57 

26  57 

17  92 

4  42 

3  23 

1  00 

1  327 

1.5  

71 

310.13 

18.65 

7.34 

3.37 

0.77 

1  605 

2  

103 

31.50 

17.97 

8.60 

3.18 

1.75 

1  775 

3  

117 

32.41 

19.86 

7.18 

3  24 

2.13 

1  470a 

4  

169 

32.77 

20  35 

6  83 

3  41 

2  18 

1  775 

5  

177 

34  88 

20  46 

8  53 

3  84 

2  05 

1  838 

6  

250 

38  83 

23  41 

9  14 

4  82 

1  46 

2  094 

7  

324 

37.73 

21.58 

10.44 

3.97 

1.74 

2  235 

PULLETS 
Ibs. 
2  

73 

31  89 

18  82 

8  82 

3  19 

1  06 

1  676 

3  

94 

34  92 

19  37 

9  97 

3  08 

2  50 

1  967 

4  

189 

38  58 

19  81 

14  29 

2  95 

1  53 

2  329 

5  

219 

40.19 

20.99 

16.19 

3.24 

—  0.23 

2  650 

CAPONS 
Ibs. 
3  

88 

32  21 

19  35 

8  51 

3  27 

1  08 

1  833 

4  

170 

34  99 

19  74 

9  74 

3  37 

2  14 

2  156 

5  

180 

37  10 

19  16 

11  68 

3  22 

3  04 

2  236 

6  

215 

40  30 

21  22 

13  41 

3  62 

2  05 

2  370 

7  

240 

41.62 

19.23 

17.78 

2.95 

1.66 

2  707 

aThe  estimated  energy  value  of  this  group,  using  average  factors  for  protein 
and  fat,  is  1,814  small  calories  per  gram. 

pounds  was  reached.  The  energy  value  per  gram  of  the  different 
samples  varied  closely  in  accordance  with  their  content  of  ether  ex- 
tract. 

From  the  relative  weights  of  the  different  samples  for  each  group 
of  birds  and  their  chemical  composition,  the  composition  of  the  live 
birds  was  calculated.  The  values  thus  obtained  are  given  in  Table 
26.  For  comparison,  the  average  composition  of  5  White  Plymouth 
Rock  chicks  shortly  after  hatching  is  given.  These  data  on  baby 


102 


BULLETIN  No.  278 


[June, 


chicks  were  obtained  in  connection  with  another  experiment.  The 
percentage  of  dry  substance  increased  very  regularly  with  advancing 
age  and  size,  attaining  higher  figures  for  the  pullets  and  capons  than 
for  the  cockerels.  On  the  other  hand,  the  percentages  of  ash  and  pro- 
tein were  generally  larger  for  the  cockerels  than  for  the  pullets  or 
capons  for  any  given  weight.  Pullets  show  a  much  more  marked  ten- 

TABLE  27 . — PERCENTAGE  COMPOSITION  OF  BIRDS  ON  BASIS  OF  EMPTY  WEIGHT 


• 


Kind  of  bird 
and  weight 

Dry 

substance 

Crude 
protein 
(Nx  6.0) 

Crude 
fat 

Ash 

Gross 
energy 
per  gram 

COCKERELS 
Ibs. 
0  5  

perct. 
29  94 

perct. 
18  77 

perct. 
4  75 

perct. 
3  00 

small  cak. 
1  474 

1  

28.92 

19.10 

6.30 

3.35 

1  598 

1  

28.19 

18.86 

4.65 

3.40 

1  404 

1.5  

31.83 

19.70 

7.75 

3.56 

1  695 

2  

32.36 

18.47 

8.83 

3.26 

1  819 

3  

33  80 

20  71 

7  49 

3  38 

1  533a 

4  

33  92 

21  07 

7  07 

3  53 

1  838 

5..  

36.17 

21.22 

8.90 

3.98 

1  908 

6  

39.97 

24.09 

9.41 

4.96 

2  149 

7  

38.61 

22.08 

10.67 

4.06 

2  213 

PULLETS 
Ibs. 
2  

33  62 

19  85 

9  19 

3  35 

1  766 

3  

36  24 

20  10 

10  35 

3  19 

2  042 

4  

39  76 

20  42 

13  61 

3  04 

2  401 

5.. 

41  90 

21  88 

16  88 

3  38 

2  762 

,cJ 

CAPONS 
Ibs. 
3  

33.68 

20  23 

8  90 

3  42 

1  916 

4  

35  98 

20  30 

10  02 

3  47 

2  217 

5  

38  11 

19  68 

12  00 

3  30 

2  297 

6  

41  76 

21  99 

13  90 

3  75 

2  456 

7  

42.90 

19.82 

18.33 

3.06 

2  790 

"The  estimated  energy  value  of  this  group,  using  average  factors  for  protein 
and  fat,  is  1,872  small  calories  per  gram. 

dency  to  fatten  than  cockerels,  the  capons  occupying  an  intermediate 
position  in  this  respect  (Table  26) .  The  energy  value  per  gram  of  the 
pullets  for  weights  of  3  pounds  or  above  were  also  distinctly  higher 
than  the  energy  values  for  either  cockerels  or  capons. 

The  close  agreement  between  the  composition  of  the  two  groups 
of  1-pound  cockerels  killed  two  weeks  apart  is  noteworthy,  indicating 
that  the  chemical  as  well  as  the  anatomical  composition  of  the  birds 
is  more  a  function  of  the  growth  attained  than  of  the  age.  In  further 
support  of  this  statement,  the  distinct  difference  in  chemical  composi- 
tion between  the  1 -pound  and  1.5-pound  cockerels  slaughtered  two 
weeks  apart  may  be  pointed  out. 


1926} 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


103 


For  some  purposes  it  is  preferable  to  express  the  chemical  com- 
position of  animals  on  the  basis  of  the  empty  weights.  This  has  been 
done  in  Table  27  for  the  birds  slaughtered  in  this  experiment.  The 
differences  between  the  values  in  Table  27  and  those  in  Table  26, 
however,  are  so  small  that  they  call  for  no  further  discussion. 

TABLE  28. — PERCENTAGE  DISTRIBUTION  OF  DRY  MATTER  AND  PROTEIN  AMONG 

(1)  EDIBLE  FLESH  AND  VISCERA,  (2)  BONES  OF  THE  DRESSED  CARCASS, 

AND  (3)  OFFAL  IN  BIRD  s  OF  DIFFERENT  WEIGHTS  AND  SEX 


Dry  matter 

Protein 

Kind  of  bird 
and  weight 

Edible 
flesh, 
etc. 

Bones  of 
dressed 
carcass 

Offal 

Edible 
flesh, 
etc. 

Bones  of 
dressed 
carcass 

Offal 

COCKERELS 
Ibs. 
0.5  

perct. 
33.6 

perct. 
23.7 

perct. 
42.7 

perct. 
37.2 

perct. 
18.6 

perct. 
44.2 

1  

35.0 

24.1 

40.9 

41.1 

16.3 

42.6 

1.5  

36.5 

22.8 

40.7 

41.2 

16.7 

42.1 

2  

33.2 

26.1 

40.7 

40.2 

18.3 

41.4 

3  

35.6 

24  8 

39.6 

41.0 

16.5 

42.5 

4  

36.1 

25.5 

38  3 

41.5 

18.0 

40.5 

5  

33.6 

24.6 

41.8 

39.7 

16.3 

44.0 

6  

32.3 

21.4 

46.3 

38.0 

13.0 

49.0 

7  

34.7 

21.1 

44.2 

45.3 

14.6 

40.0 

PULLETS 
Ibs. 
2  

32  9 

23  9 

43  2 

39  7 

16  2 

44.1 

3  

41  6 

21  1 

37  2 

41  6 

15  5 

42.9 

4...    . 

35  9 

19  5 

44  5 

42  1 

13  0 

44  8 

5  

37.7 

19.3 

42.9 

43.4 

12.7 

43.9 

CAPONS 
Ibs. 
3  

36.0 

23.8 

40  2 

42.0 

16.3 

41.7 

4  

33.1 

25.0 

41  9 

38.6 

17.3 

44.1 

5  

36  2 

23  4 

40  4 

41  1 

17.6 

41.3 

6  

33.4 

20  6 

45  9 

38  0 

14  6 

47.4 

7  

41.3 

19.6 

39.1 

43.5 

13.9 

42.6 

The  distribution  of  dry  matter,  protein,  ether  extract,  energy,  and 
mineral  matter  among  the  three  composite  samples  is  expressed  in  per- 
centages in  Tables  28,  29,  and  30.  The  offal  sample  contained  a  large 
proportion,  namely  from  40  to  50  percent  (average  41.7  percent),  of 
the  dry  substance  in  the  birds  at  all  weights.  Furthermore,  there  is 
no  clear  distinction  between  the  different  groups  of  birds  in  this  re- 
spect, nor  can  any  progressive  change  in  the  percentage  be  noted  with 
increasing  size  and  age.  The  edible  part  of  the  carcass  contains  an 
average  of  35.5  percent  of  the  total  dry  matter,  40.8  percent  of  the 
total  protein,  30.2  percent  of  the  total  ether  extract,  and  37.2  percent 
of  the  total  gross  energy  of  the  birds  at  all  weights.  For  the  pullets, 


104 


BULLETIN  No.  278 


[June, 


the  percentage  of  the  total  fat  and  energy  contained  in  the  edible 
flesh  and  viscera  seemed  to  be  distinctly  larger  for  weights  of  3  pounds 
and  over,  than  the  similar  percentages  for  the  cockerels  and  capons. 
The  mineral  matter  in  the  carcasses  was  contained  largely  in  the  bone 
sample,  which  contained  an  average  of  61.1  percent.  The  offal  sample 
ranked  next  with  an  average  of  24.2  percent,  and  the  edible  flesh 

TABLE  29.— PERCENTAGE  DISTRIBUTION  OF  ETHER  EXTRACT  AND  GROSS  ENERGY 
AMONG   (1)  EDIBLE  FLESH  AND  VISCERA,   (2)   BONES  OF  THE  DRESSED 
CARCASS,   AND    (3)    OFFAL  IN   BIRDS   OF   DIFFERENT  WEIGHTS 
AND  SEX 


] 

3ther  extrac 

t 

Gross  energ 

y 

Amd.  01 
bird  and 
weight 

Edible 
flesh, 
etc. 

Bones  of 
dressed 
carcass 

Offal 

Edible 
flesh, 
etc. 

Bones  of 
dressed 
carcass 

Offal 

COCKERELS 
Ibs. 
0.5  

perct. 
30  9 

perct. 
17.1 

perct. 
52  0 

perct. 
34.6 

perct. 
20.8 

perct. 
44.7 

1  

27  3 

26  1 

46  7 

35  0 

20  2 

44  8 

1.5  

34  2 

19  5 

46  3 

36  9 

18  3 

44  8 

2  

27.5 

31.8 

40.7 

34.7 

23.4 

41.9 

3  

24.8 

29.0 

46  2 

43.2 

24.8 

32.0 

4  

23.1 

33  1 

43  9 

33  1 

22  8 

44  1 

5  

26  6 

27  9 

45  6 

37  0 

22  2 

40  8 

6  

26.0 

25.6 

48.4 

36.1 

19.1 

44.8 

7  

19.9 

18.4 

61.6 

34.6 

16.8 

48.6 

PULLETS 
Ibs.  j 
2...L  

27  1 

26  2 

46  7 

35  5 

21  5 

43  0 

3  

41  7 

22  7 

35  6 

40  3 

18  5 

41  2 

4  

35.3 

18.6 

46.1 

43.7 

15.6 

40.7 

5  

35.1 

17.5 

47.4 

40  0 

15.8 

44.2 

CAPONS 
Ibs. 
3.    ... 

29  0 

27  2 

43  8 

36  6 

21  0 

42  4 

4  

29.2 

26.1 

44.9 

32.7 

21.6 

45.7 

5  

29.9 

24.9 

45.1 

34.4 

21  2 

44.4 

6..  . 

32.8 

18  7 

48  4 

37  0 

18  0 

45  0 

7  

44.0 

18.8 

37.2 

43.7 

16.6 

39.7 

sample  contained  only  14.7  percent.  In  general,  the  percentage  of  the 
mineral  matter  of  the  carcass  contained  in  the  bones  of  the  dressed 
carcass  tended  to  increase  with  increasing  size  and  age,  while  the  per- 
centage contained  in  the  offal  tended  to  decrease. 

From  the  chemical  composition  of  the  flesh  and  fat  of  the  dressed 
carcass  and  of  the  edible  viscera  (exclusive  of  heart  and  kidneys) ,  and 
from  the  weights  of  this  fraction  of  the  carcass  (corrected  to  even  body 
weights) ,  the  total  edible  nutrients  in  White  Plymouth  Rock  chickens 
of  different  live  weights  may  be  calculated.  The  results  of  such  a  cal- 
culation are  given  in  Table  31.  The  outstanding  feature  of  this  tab- 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


105 


ulation  is  the  demonstration  of  the  superiority  of  pullets  in  their  con- 
tent of  edible  fat  and  energy,  unaccompanied  by  any  inferiority  in  the 
content  of  edible  protein.  Capons  rank  next  to  pullets  in  regard  to 
the  content  of  edible  fat  and  energy,  but  are  inferior  to  cockerels  in 
the  content  of  edible  protein. 

Altho  the  different  groups  of  birds  were  killed  at  average  weights 
approximating  closely  the  weights  given  in  the  left  column  of  the 
tables  just  considered,  it  was  only  an  approximation.  In  computing 


TABLE  30. — PERCENTAGE  DISTRIBUTION  OF  MINERAL  MATTER  AMONG  (1)  EDIBLE 
FLESH  AND  VISCERA,  (2)  BONES  OF  THE  DRESSED  CARCASS,  AND  (3)  OFFAL 
IN  BIRDS  OF  DIFFERENT  WEIGHTS  AND  SEX 


Crude  ash 

Kind  of  bird 
and  weight 

Edible 
flesh, 
etc. 

Bones  of 
dressed 
carcass 

Offal 

COCKERELS 
Ibs. 
0.5  

perct. 
16.1 

perct. 
52.2 

perct. 
31.7 

1  

15.2 

57.1 

27.7 

1.5  

14.4 

60.1 

25.5 

2  

13.0 

60.4 

26.7 

3  

14.1 

61.6 

24.3 

4  

12.0 

68.1 

19.8 

5  

13.9 

67.8 

18.4 

6  

15.7 

55.4 

28.9 

7  

16.4 

62.0 

21.6 

PULLETS 
Ibs. 
2  

13.0 

60.1 

26.9 

3  

16  6 

54.5 

28.9 

4  

15.4 

62.6 

22.1 

5  

18.8 

62.5 

18.7 

CAPONS 
Ibs. 
3  

16.0 

57.1 

26.9 

4  

13.0 

65.5 

21.5 

5  

14  8 

64.8 

20.4 

6  

11   6 

66.3 

22.1 

7  

14.7 

61.6 

23.7 

the  composition  of  gains  within  any  weight  interval  of  the  cockerels, 
pullets,  and  capons,  it  is  necessary  to  compute  the  composition  of 
birds  at  the  exact  weights  under  consideration.  This  is  done  in  Table 
32  by  applying  the  percentages  contained  in  Table  26  to  the  even 
weights  of  .5,  1,  1.5,  and  2  pounds,  etc.  The  total  energy  content  per 
bird  has  been  estimated  (at  each  weight)  from  the  content  of  the  crude 
protein  and  crude  fat  (Table  32,  last  column) .  In  this  estimation  the 
energy  values  of  protein  and  fat  have  been  taken  as  5.7  and  9.5  cal- 


106 


BULLETIN  No.  278 


[June, 


ories  per  gram,  respectively.  These  factors  have  been  used  by  Armsby 
for  similar  computations  on  the  larger  farm  animals.  A  comparison 
of  this  column  of  figures  with  the  gross  energy  content  as  directly  de- 
termined gives  some  idea  concerning  the  size  of  error  that  would  be 
made  in  applying  these  average  factors  to  the  protein  and  fat  of 
chicken  carcasses.  As  a  general  rule,  the  estimated  energy  content  is 
higher  than  the  content  as  directly  determined,  the  average  difference 
amounting  to  3.6  percent. 


TABLE  31.- 


-EDIBLE  NUTRIENTS  IN  WHITE  PLYMOUTH  ROCK  BIRDS  OF  DIFFERENT 
WEIGHTS  AND  SEX 


Kind  of 
bird  and 
weight 

Weight  of 
flesh  and 
edible 
viscera 

Dry 

matter 

Crude 
protein 

Crude 
fat 

Ash 

Gross 
energy 

COCKERELS 
Ibs. 
0.5  

gms. 
64 

gms. 
19  4 

gms. 
13  4 

gms. 
2  8 

gms. 
0  9 

cals. 
98 

1  

166 

42.1 

32.4 

6.5 

2.1 

242 

1>           .    .  . 

177 

43  9 

34  6 

6  3 

2  3 

226 

1.5  

254 

72.6 

50.8 

16  6 

3  2 

391 

2  

348 

94  8 

65  6 

21  5 

3  7 

556 

3  

551 

157 

111 

24.2 

6.2 

866 

4  

729 

215 

153 

28  6 

7  4 

1  064 

5  

934 

266 

184 

51.7 

12.0 

1  542 

6  

1  198 

342 

242 

64  7 

20.6 

2  053 

7  

1  480 

416 

311 

66  0 

20  7 

2  376 

PULLETS 
Ibs.  } 
2  

356 

95.2 

67.8 

21.4 

3.8 

540 

3  

580 

198 

110 

56  6 

6.1 

1  079 

4  

811 

250 

150 

91  0 

8  2 

1  834 

5  

1  022 

344 

207 

129 

13  8 

2  408 

CAPONS 
Ibs. 
3  

561 

158 

111 

33.6 

7.1 

913 

4  

718 

210 

138 

51  4 

8.0 

1  283 

5  

922 

305 

179 

79  4 

10  8 

1  745 

6  

1  166 

366 

220 

120 

11  4 

2  389 

7  

1  477 

546 

266 

249 

13.9 

3  755 

The  data  in  Table  32  must  form  the  basis  for  the  estimation  of 
the  composition  of  successive  gains  in  weight  of  the  birds  from  .5  to 
7  pounds.  They  are  too  irregular,  however,  to  permit  of  accurate  esti- 
mates, mainly  because  of  the  small  size  of  the  groups  of  birds  ana- 
lyzed at  each  weight.  Under  these  circumstances  it  is  to  be  expected 
that  the  error  in  computing  the  composition  of  successive  small  gains 
in  weight  from  such  data  would  be  considerable.  For  example,  the 
error  in  assuming  that  the  5  cockerels  killed  and  analyzed  at  a  weight 
of  5  pounds  possessed  the  same  composition  at  a  weight  of  4  pounds 


THE  GROWTH  OP  WHITE  PLYMOUTH  ROCK  CHICKENS 


107 


as  the  5  other  cockerels  killed  at  that  weight,  will  be  contained  in  full 
in  the  estimate  of  the  composition  of  the  gain  from  4  to  5  pounds. 
This  error,  inherent  in  slaughter  experiments  of  this  type,  may  be  de- 
creased only  by  increasing  the  number  of  birds  killed  at  each  weight 
or  by  smoothing  off  the  data  obtained  on  the  smaller  groups  of  birds 
by  the  proper  mathematical  procedure.  The  latter  expedient  was 
adopted,  and  it  was  found  that  the  relation  between  the  content  of 
the  birds  in  dry  matter,  protein,  etc.,  and  the  live  weight  of  the  bird, 

TABLE  32. — CALCULATED  COMPOSITION  OP  THE  BIRDS  AT  EVEN  WEIGHTS 


Kind  of 
bird  and 
weight 

Dry 

sub- 
stance 

Crude 
protein 
(Nx  6.0) 

Crude 
fat 

Ash 

Unac- 
counted 
for 

Gross 
energy 

Esti- 
mated 
gross 
energy" 

COCKERELS 
Ibs. 
0.5  

gms. 
63 

gms. 
40 

gms. 
10 

gms. 
6 

gms. 

7 

therms 
0  31 

therms 
0  32 

1  

121 

81 

23 

14 

3 

0  64 

0  68 

1.5  

205 

127 

50 

23 

5 

1  09 

1  20 

2  

286 

163 

78 

29 

16 

1  61 

1  67 

3  

441 

270 

98 

44 

29 

2  00 

2  47 

4  

594 

369 

124 

62 

39 

3  22 

3  28 

5  

791 

464 

195 

86 

46 

4  32 

4  50 

6  

1  057 

637 

249 

131 

40 

5  70 

6  00 

7  

1  198 

685 

331 

126 

56 

7  10 

7  05 

PULLETS 
Ibs. 
2  

289 

171 

80 

29 

9 

1  52 

1  73 

3  

475 

264 

136 

42 

33 

2  68 

2  80 

4  

700 

359 

259 

54 

28 

4  22 

4  51 

5  

912 

476 

367 

74 

—  5 

6  01 

6  20 

CAPONS 
Ibs. 
3  

438 

263 

116 

45 

14 

2  49 

2  60 

4  

635 

358 

177 

61 

39 

3  91 

3  72 

5  

842 

435 

265 

73 

69 

5  07 

5  00 

6  

1  097 

578 

365 

99 

55 

6  45 

6  76 

7  

1  322 

611 

565 

94 

52 

8.59 

8.85 

"These  values  were  estimated  by  using  factors  5.7  calories  per  gram  for  protein 
and  9.5  calories  per  gram  for  fat. 

can  be  very  well  represented  for  the  range  of  live  weight  included  in 
this  experiment  by  a  parabolic  equation  of  the  type  y  =  ax  -\-  bx2. 

This  equation  has  been  fitted  to  each  of  the  relations  between  the 
different  chemical  constituents  and  live  weight  for  each  of  the  three 
groups  of  birds.  In  dealing  with  the  results  for  pullets  and  capons, 
it  has  been  assumed  that  pullets  weighing  less  than  2  pounds  would 
have  the  same  composition  as  cockerels  of  equal  weight,  and  that  the 
composition  of  capons  before  castration  is  well  represented  by  the 
composition  of  the  cockerels  slaughtered  between  .5  and  2  pounds  in- 
clusive. The  equation  has  been  fitted  to  each  set  of  experimental  data 


108 


BULLETIN  No.  278 


[June, 


by  the  method  of  least  squares.  A  graphical  picture  of  the  closeness 
of  fit  of  the  mathematical  curves  to  the  experimental  data  is  given  in 
Figs.  1  to  5  inclusive.* 

An  inspection  of  these  charts  seems  to  indicate  that  the  closeness 
of  fit  of  the  curves  to  the  experimental  data  is  satisfactory.  The  fact 
that  the  relation  between  the  content  of  these  birds  in  any  given  nutri- 
ent, and  the  slaughter  weight,  is  such  that  it  can  well  be  represented 
by  a  mathematical  equation  of  this  simple  type,  again  testifies  to  the 

TABLE  33. — COMPOSITION  OF  THE  BIRDS  AT  EVEN  WEIGHTS  AS  COMPUTED  FROM 
MATHEMATICAL  EQUATIONS  FITTED  TO  THE  DATA  IN  TABLE  31 


Kind  of 
bird  and 
weight 

Dry 

substance 

Crude 
protein 

Crude 
fat 

Ash 

Unac- 
counted 
for 

Gross 
energy 

COCKERELS 
Ibs. 
0  5... 

gms. 
64  2 

gms. 
41.2 

gms. 
12.4 

gms. 
6.7 

gms. 
3.9 

cals. 
290 

1  

131.7 

83.5 

26.4 

13.7 

8.1 

615 

1.5  

202.4 

127.1 

42.0 

21.1 

12.2 

971 

2..  

276.5 

171.9 

59.2 

28.9 

16.5 

1  361 

3  

434.4 

265.1 

98.5 

45.5 

25.3 

2  239 

4  

605.4 

363.1 

144.4 

63.6 

34.3 

3  249 

5  

789.4 

465.9 

196.6 

83.1 

43.8 

4  390 

6  

986.6 

573.6 

255.4 

104.0 

53  6 

5  663 

7  

1  196.9 

686.1 

320.7 

126.4 

63.7 

7  067 

8  

1  420.3 

803.4 

392.4 

150.5 

74.0 

8  603 

PULLETS 
Ibs. 
0.5..?.  

62.6 

39.8 

9.6 

6.8 

6.4 

276 

1  

131.8 

81.2 

25.4 

13.8 

11.4 

624 

1.5  

207.5 

124.3 

47.2 

20.8 

15  2 

1  043 

2  

289.8 

169.1 

75.1 

27.9 

17.7 

1  534 

3  

474.1 

263.7 

149.2 

42.4 

18.8 

2  732 

4  

684.6 

365.0 

247.7 

57.1 

14.8 

4  218 

5  

921.4 

472.9 

370.5 

72.2 

5.8 

5  990 

6  

1  184.5 

587.5 

517.7 

87.6 

-8.3 

8  050 

CAPONS 
Ibs. 
0.5  

61.1 

43.0 

6.4 

8.0 

3  7 

313 

1  

127.5 

86.0 

17.7 

15.8 

8.0 

671 

1.5  

199.1 

129.3 

33  8 

23  4 

12  6 

1  073 

2  

275.9 

172.6 

54.7 

30.9 

17.7 

1  520 

3  

445.4 

259.8 

111.0 

45.2 

29.4 

2  546 

4  

635.9 

347.4 

186.7 

58.8 

43.0 

3  750 

5  

847.3 

435.6 

281.7 

71.6 

58.4 

5  132 

6... 

1  079.8 

524.4 

396.1 

83  7 

75  6 

6  692 

7  

1  333.3 

613.7 

529.8 

95  1 

94  7 

8  430 

8  

1  607.8 

703.5 

682.9 

105.7 

115.7 

10  346 

*Jn  determining  the  constants  of  the  equations,  no  account  was  taken  of 
the  experimental  data  for  the  6-pound  cockerels  relating  to  dry  matter,  crude 
protein,  and  ash,  or  of  the  data  for  the  6-pound  capons  relating  to  protein  and 
ash.  These  results  appear  to  be  so  far  out  of  line  with  the  others  as  to  justify 
their  exclusion. 


1926] 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


109 


no 


BULLETIN  No.  278 


[June, 


9  uj 


-•  O 


1926] 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


111 


conclusion  that  the  composition  of  birds  is  more  closely  related  to  the 
growth  attained  than  to  the  age. 

By  means  of  the  mathematical  equations  fitting  the  various  sets 
of  experimental  results  contained  in  Table  32,  it  is  possible  to  estimate 
the  composition  of  birds  at  even  weights,  obtaining  in  this  way  a 
smoothed  set  of  data  from  which  the  composition  of  successive  gains 
may  be  computed  with  greater  accuracy  than  from  the  unsmoothed 
experimental  data  themselves.  This  has  been  done  in  Table  33.  The 


Body    Weight  of    Cockerels    in    Pounds 
_z A       3       6       7       6 


945676 

Body   Weight    of    Capons  in  Pounds 


FIG.  5 

composition  of  the  three  groups  of  birds  at  weights  1  pound  heavier 
than  the  greatest  actual  slaughter  weight  has  been  estimated  by  the 
mathematical  equations.  Any  more  extensive  extrapolation,  however, 
would  not  be  advisable.  Corrected  estimates  of  the  percentage  com- 
position of  the  birds  at  successive  even  weights  may  be  computed 
from  the  data  in  Table  33.  This  has  been  done  in  Table  34.  Table  35 
contains  the  estimates  of  the  composition  of  the  successive  pound  gains 
in  weight  of  cockerels,  pullets,  and  capons  based  upon  the  smoothed 
data  contained  in  Table  33.  The  content  of  the  successive  pound  gains 


112 


BULLETIN  No.  27S 


[June, 


in  dry  matter,  protein,  fat,  ash,  and  energy  increases  in  a  linear  fashion 
with  the  live  weight  of  the  birds,  a  result  which  follows  from  the  fact 
that  the  relation  between  the  content  of  the  birds  in  each  of  these 
constituents  and  the  live  weight  may  be  represented  by  a  parabolic 
equation.* 

It  is  evident  that  the  energy  value  of  the  gains  put  on  by  pullets 
exceeds  the  energy  value  of  gains  for  the  other  two  groups  of  birds, 
while  the  capon  gains  rank  next  in  this  respect.  For  example,  the  gain 
from  4  to  5  pounds  on  the  pullets  contained  a  decidedly  greater  gross 
energy  content  than  the  7-  to  8-pound  gain  on  the  cockerels,  and  was 


TABLE  34. — PERCENTAGE  COMPOSITION  OF  THE  BIRDS  AT  EVEN  WEIGHTS  COMPUTED 

FROM  TABLE  33 


Kind  of  bird 
and  weight 

Dry 

substance 

Crude 
protein 

Crude 
fat 

Ash 

Unac- 
counted 
for 

Gross 
energy 
per  gram 

COCKERELS 
Ibs. 
0.5  

perct. 
28.31 

perct. 
18.17 

perct. 
5.47 

perct. 
2.95 

perct. 
1.72 

small  cals. 
1  279 

1  

29.03 

18.41 

5.82 

3.02 

1.78 

1  356 

1.5  

29  75 

18  68 

6  17 

3.10 

1  80 

1  427 

2  

30.48 

18.95 

6.53 

3.19 

1.81 

1  500 

3  

31.92 

19.48 

7.24 

3.34 

1.86 

1  645 

4  

33.37 

20.01 

7.96 

3.51 

1.89 

1  791 

5  

34.81 

20.54 

8.67 

3.66 

1.94 

1  936 

6  

36.25 

21.08 

9.38 

3.82 

1.97 

2  081 

7  

37.70 

21.61 

10  10 

3.98 

2.01 

2  226 

8...J  

39.14 

22.14 

10.81 

4.15 

2.04 

2  371 

PULLETS 
Ibs. 
0.5  

27.60 

17  55 

4  23 

3  00 

2.82 

1  217 

1  

29.06 

17.90 

5.60 

3.04 

2.52 

1  376 

1.5  ,. 

30.50 

18.27 

6.94 

3.06 

2.23 

1  533 

2  

31.94 

18.64 

8  28 

3.08 

1.94 

1  691 

3  

34.84 

19  38 

10  96 

3  12 

1.38 

2  008 

4  

37.73 

20.12 

13  65 

3  15 

0  81 

2  325 

5  

40.63 

20.85 

16.34 

3.18 

0.26 

2  641 

6  

43.52 

21.59 

19.02 

3.22 

-0.31 

2  958 

CAPONS 
Ibs 
0.5  

26.94 

18.96 

2  82 

3  53 

1  63 

1  380 

1  

28.11 

18.96 

3.90 

3.48 

1.77 

1  479 

1.5  

29  26 

19  00 

4  97 

3  44 

1  85 

1  577 

2  

30.41 

19.03 

6  03 

3  41 

1.94 

1  675 

3  

32.73 

19.09 

8  16 

3  32 

2  16 

1  871 

4  

35.05 

19.15 

10  30 

3  24 

2  36 

2  067 

5  

37  36 

19  21 

12  42 

3  16 

2  57 

2  263 

6  

39  68 

19  27 

14  55 

3  08 

2  78 

2  459 

7  

41  99 

19  33 

16  69 

3  00 

2  97 

2  655 

8  

44.31 

19.39 

18.82 

2.91 

3.19 

2  851 

*See  Lipka,  J.,  "Graphical  and  Mechanical  Computation,"  p.  146. 
Wiley  and  Sons,  1918. 


John 


1926} 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


113 


slightly  greater  than  the  6-  to  7-pound  gain  on  the  capons.  This  re- 
lation of  the  energy  content  of  gains  is  directly  related  to  their  content 
in  crude  fat.  Evidently  pullets  fatten  at  a  much  more  rapid  rate 
than  either  cockerels  or  capons.  As  an  illustration  of  this  fact, 
the  5-  to  6-pound  gain  on  the  pullets  contained  over  twice  as 
much  fat  as  the  7-  to  8-pound  gain  on  the  cockerels.  At  the  same 
time,  the  pullet  gains  contained  larger  amounts  of  protein  than  the 

TABLE  35. — COMPOSITION  OF  SUCCESSIVE  POUND  GAINS  IN   WEIGHT  COMPUTED 

FROM  TABLE  33 


Kind  of 
bird 

Gain 
from 

Dry  sub- 
stance 

Crude 
protein 

Crude 
fat 

Ash 

Unac- 
counted 
for 

Gross 
energy 

COCKERELS  

Ibs. 
0  to  1 

gms. 
131.7 

gms. 
83.5 

gms. 
26  4 

gms. 
13  7 

gms. 
8  1 

cals. 
615 

PULLETS  

1  to  2 
2  to  3 
3  to  4 
4  to  5 
5  to  6 
6  to  7 
7  to  8 

0  to  1 

144.8 
158.1 
171.0 
184.0 
197.2 
210.3 
223  A 

131  8 

88.4 
93.2 
98.0 
102.8 
107.7 
112.5 
117.3 

81  2 

32.8 
39.3 
45.9 
52.2 
58.8 
65.3 
71.7 

25  4 

15.2 
16.6 
18.1 
19.5 
20.9 
22.4 
24.1 

13  8 

8.4 
9.0 
9.0 
9.5 
9.8 
10.1 
10.3 

11  4 

746 
878 
1  010 
1  141 
1  273 
1  404 
1  536 

624 

CAPONS  

1  to  2 
2  to  3 
3  to  4 
4  to  5 
5  to  6 

0  to  1 

158.0 
184.3 
210.5 
236.8 
263.1 

127  5 

87.9 
94.6 
101.3 
107.9 
114.6 

86  0 

49.7 
74.1 
98.5 
122.8 
147.2 

17  7 

14.1 
14.5 
14.7 
15.1 
15.4 

15  8 

6.3 
1.1 
-4.0 
-9.0 
-14.1 

8  0 

910 
1  198 
1  486 
1  772 
2  060 

671 

1  to  2 
2  to  3 
3  to  4 
4  to  5 
5  to  6 
6  to  7 
7  to  8 

148.4 
169.5 
190.5 
211.4 
232.5 
253.5 
274.5 

86.6 

87.2 
87.6 
88.2 
88.8 
89.3 
89.8 

37.0 
56.3 
75.7 
95.0 
114.4 
133.7 
153.1 

15.1 
14.3 
13.6 
12.8 
12.1 
11.4 
10.6 

9.7 
11.7 
13.6 
15.4 
17.2 
19.1 
21.0 

849 
1  026 
1  204 
1  382 
1  560 
1  738 
1  916 

cockerel  gains,  the  capon  gains  ranking  last  in  this  respect.  This  is 
probably  related  to  the  fact  that  the  growth  of  the  pullets  represented 
more  of  an  increase  in  muscular  tissue  and  less  of  an  increase  in  bone 
than  the  growth  of  the  cockerels. 

It  is  interesting  to  note  that  the  protein  content  of  the  capon  gains 
was  very  nearly  constant  thruout  the  range  of  growth  covered  in 
this  experiment.  On  the  other  hand,  the  cockerels  outranked  all  other 
birds  in  the  ash  content  of  their  gains,  which  increased  markedly, 
while  the  ash  content  of  the  pullet  gains  was  very  nearly  constant. 
The  computed  ash  content  of  the  capon  gains  decreased  from  begin- 
ning to  end,  but  the  authors  do  not  attach  any  great  significance 
to  this  apparent  decrease,  because  it  was  evidently  dependent  upon 
whether  or  not  the  erratic  result  on  the  6-pound  capons  was  consid- 


114 


BULLETIN  No.  278 


[June, 


ered  in  determining  the  constants  in  the  parabolic  equation  relating 
to  the  crude  ash  content  of  the  birds.  The  dry  matter  content  of  the 
pullet  gains  exceeded  slightly  the  dry  matter  content  of  the  capon 
gains  at  equal  weight  intervals,  and  greatly  exceeded  the  dry  matter 
content  of  the  cockerel  gains. 

The  results  compiled  in  Table  35  are  expressed  on  a  percentage 
basis  in  Table  36.    These  figures  reveal  the  same  relationships  that 


TABLE  36. — PERCENTAGE  COMPOSITION  OF  SUCCESSIVE  POUND  GAINS  IN  WEIGHT 
COMPUTED  FROM  TABLE  35 


Kind  of  bird 

Gain 
from 

Dry  sub- 
stance 

Crude 
protein 

Crude 
fat 

Ash 

Unac- 
counted 
for 

Gross 
energy 
per  gram 

COCKERELS  

Zfe. 

0  to  1 

perct. 
29  03 

perct. 
18.41 

perct. 
5  82 

perct. 
3  02 

perct. 
1  78 

small 
cals. 
1  356 

PULLETS  

1  to  2 
2  to  3 
3  to  4 
4  to  5 
5  to  6 
6  to  7 
7  to  8 

0  to  1 

31.92 
34.85 
37.70 
40.57 
43.47 
46.36 
49.25 

29  06 

19.49 
20.55 
21.60 
22.66 
23.74 
24.80 
25.86 

17  90 

7.23 
8.66 
10.11 
11.50 
12.96 
14.40 
15.81 

5  60 

3.35 
3.66 
3.99 
4.30 
4.61 
4.94 
5.31 

3  04 

1.85 
1.98 
2.00 
2.11 
2.16 
2.22 
2.27 

2  52 

1  645 
1  936 
2  227 
2  515 
2  806 
3  095 
3  386 

1  376 

^ 
CAPONS  

1  to  2 
2  to  3 
3  to  4 
4  to  5 
5  to  6 

0  to  1 

34.83 
40.63 
46.41 
52.20 
58.00 

28  11 

19.38 
20.86 
22.33 
23.79 
25.26 

18  96 

10.96 
16.34 
21.72 
27.07 
32.45 

3  90 

3.11 
3.20 
3.24 
3.33 
3.40 

3  48 

1.38 
0.23 
-0.88 
-1.99 
-3.11 

1  77 

2  006 
2  641 
3  276 
3  907 
4  541 

1  479 

1  to  2 
2  to  3 
3  to  4 
4  to  5 
5  to  6 
6  to  7 
7  to  8 

32.72 
37.37 
42.00 
46.61 
51.26 
55.89 
60.52 

19.09 
19.22 
19.31 
19.44 
19.58 
19.69 
19.80 

8.16 
12.41 
16.69 
20.94 
25.22 
29.48 
33.75 

3.33 
3.15 
3.00 
2.82 
2.67 
2.51 
2.34 

2.14 
2.59 
3.00 
3.41 
3.79 
4.21 
4.63 

1  872 
2  262 
2  654 
3  047 
3  439 
3  832 
4  224 

have  already  been  pointed  out.  The  change  in  percentage  composi- 
tion of  gains  with  increasing  body  weight  is  illustrated  graphically  in 
Figs.  6  and  7. 

RATE  OF  RETENTION  OF  NUTRIENTS  DURING  GROWTH 

The  practical  value  of  estimates  of  the  composition  of  gains  in 
weight  of  growing  animals  depends  upon  the  possibility  of  determin- 
ing from  such  data  the  requirements  of  growing  animals  for  nutri- 
ment. It  seems  obvious  that  the  amount  of  energy  added  to  the  body 
of  a  growing  animal  daily  at  different  ages  is  a  fair  estimate  of  the 
amount  of  net  food  energy  required,  above  that  used  for  maintenance, 


1926] 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


115 


s 


O 

s 

£ 


Qfl 


-CD 


116  BULLETIN  No.  278  [June, 

to  sustain  normal  growth.  Such  values  have  been  used  in  this  way 
by  Armsby  in  computing  his  feeding  standards  for  growth  and  fat- 
tening. Obviously  they  are  of  practical  significance  only  when  the 
net  energy  value  of  ordinary  farm  feeds  in  covering  growth  require- 
ments is  known.  Nevertheless,  the  determination  of  the  daily  reten- 
tion of  energy  by  growing  animals  is  a  necessary  step  in  any  accurate 
system  of  expressing  the  nutritive  requirements  of  such  animals. 

It  seems  a  logical  extension  of  Armsby's  system  to  take  the  daily 
retention  of  protein  and  mineral  matter  as  a  scientific  measure  of  the 
needs  of  growing  animals  for  these  nutrients,  even  tho  Armsby  him- 
self did  not  extend  his  energy  conceptions  in  this  manner.  It  is  per- 
haps no  idle  hope  that  some  day  it  will  be  possible  to  express  the  net 
protein  value  of  feeds  for  growth  in  a  manner  quite  analogous  to  the 
expression  of  their  net  energy  values.  Less  optimism  must  be  felt  that 
the  mineral  values  of  feeds  can  ever  be  so  simply  expressed. 

The  calculation  of  the  daily  retention  of  nutrients  by  White  Ply- 
mouth Rock  birds  evidently  .depends  upon  two  determinations:  first, 
the  determination  of  the  composition  of  successive  gains  in  weight; 
and  second,  the  determination  of  the  rate  of  gain  in  weight  at  differ- 
ent ages.  The  results  of  the  former  determination  have  already  been 
considered.  The  latter  determination  must  evidently  depend  upon 
the  data  given  in  Table  1.  However,  there  is  the  same  objection  to 
using  the  original  observations  contained  in  this  table  as  there  was 
to  the  use  of  the  experimental  results  contained  in  Table  32.  This 
objection  rests  in  the  fact  that  experimental  observations  upon 
animals  are  subject  to  a  considerable  variation  produced  by  casual 
factors,  related  either  to  the  animal  or  to  its  environment,  that  can- 
not be  brought  under  experimental  control.  These  casual  variations 
render  uncertain  to  some  degree  the  significance  of  any  single  experi- 
mental observation.  In  removing  this  type  of  variation  as  it  relates 
to  the  data  on  the  composition  of  the  birds  at  increasing  live  weights, 
given  in  Table  32,  the  method  used  was  to  fit  a  mathematical  curve 
to  the  experimental  data.  The  same  method  will  be  used  in  smooth- 
ing out  the  growth  observations  on  the  entire  flock  of  White  Plymouth 
Rock  birds. 

The  mathematical  procedure,  however,  is  not  so  simple  in  this 
case,  because  the  growth  data  are  not  so  readily  represented  by  a 
simple  mathematical  equation  as  were  the  chemical  data.  It  has  been 
previously  pointed  out  that  the  rate  of  growth  of  the  birds  exhibited 
a  more  or  less  periodical  fluctuation.  The  first  point  to  settle,  there- 
fore, in  smoothing  off  the  data,  is  whether  these  periodical  fluctuations 
are  entirely  casual  in  so  far  as  they  relate  simply  to  uncontrolled  en- 
vironmental factors,  or  whether  they  are  related  to  the  growth  of 
White  Plymouth  Rock  birds  regardless  of  environmental  changes.  The 
authors  have  already  expressed  a  hesitancy  in  attaching  any  great  sig- 


1926]  THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS  117 

nificance  to  these  fluctuations,  because  they  cannot  be  interpreted 
either  one  way  or  the  other  with  any  degree  of  assurance,  since  it  is  an 
undoubted  fact  that  weather  conditions  show  a  periodical  variation. 

The  belief  that  uncontrolled  environmental  factors  may  entirely 
account  for  the  apparent  cyclic  property  of  the  growth  curve  of  White 
Plymouth  Rock  birds  is  strengthened  by  a  comparison  of  the  Illinois 
data  with  those  obtained  at  the  Purdue  Agricultural  Experiment  Sta- 
tion, to  which  reference  has  already  been  made.  In  Figs.  8  and  9  such 
a  comparison  is  made  graphically.  In  these  charts  the  successive  bi- 
weekly gains  in  weight  expressed  in  grams  are  represented  by  rect- 
angles of  proportionate  size.  In  the  case  of  the  Illinois  data  two  suc- 
cessive biweekly  gains  have  occasionally  been  combined  in  an  at- 
tempt to  smooth  out  some  particularly  irregular  variation  in  the  rate 
of  growth.  The  Purdue  data  have  been  interpreted  by  Kempster  and 
Henderson11  as  indicating  the  existence  of  two  cycles  of  growth.  This 
interpretation  is  illustrated  by  the  curve  roughly  drawn  thru  the  tops 
of  the  rectangles  in  the  different  sections  of  Fig.  9.  These  curves  have 
been  patterned  as  closely  as  possible  after  the  curves  drawn  by  the 
above  mentioned  authors  in  illustrating  their  conclusion.  On  the  other 
hand,  the  Illinois  data  obviously  cannot  be  considered  as  supporting 
any  theory  that  the  growth  of  White  Plymouth  Rock  birds  exhibits 
only  two  cycles.  The  growth  obtained  may,  in  fact,  be  better  repre- 
sented by  an  assumption  of  three  cycles,  as  illustrated  by  the  irregular 
curves  drawn  thru  the  tops  of  the  rectangles  in  Fig.  8. 

The  marked  discrepancy  between  these  two  sets  of  growth  data 
obtained  on  birds  of  the  same  breed  may  be  taken  to  indicate  that 
the  cycles  of  growth  observed  are  more  probably  related  to  periodical 
variations  in  environmental  factors  than  to  periodical  variations  in 
the  growth  impulse  itself.  It  was  decided,  therefore,  to  smooth  off  the 
growth  data  without  regard  to  these  periodical  fluctuations  in  the  rate 
of  growth.  The  growth  curve  of  both  the  Illinois  and  Purdue  flocks 
is  generally  of  an  elongated  S  type,  but  unfortunately  it  cannot  be 
represented  thruout  its  entire  range  by  the  S  type  curve  used  by 

/£ 

Robertson12,  i.e.,  log =  K  (t  —  tj  in  which  x  is  the  growth  ac- 

A  —x 

complished  at  any  time,  t,  A  is  a  constant  equal  to  the  maximum  value 
of  x,  and  ^  is  a  constant  equal  to  t  when  x  equals  one-half  A.  When 
this  equation  is  fitted  to  the  entire  growth  data  of  either  investigation, 
a  very  poor  fit  results  for  ages  of  12  weeks  or  less.  The  expedient  finally 
used  in  overcoming  this  error,  therefore,  was  to  fit  the  above  equation 
first,  to  the  first  10  or  12  weeks  of  growth,  and  second,  to  the  growth 
subsequent  to  this  period.  The  equations  obtained  by  this  procedure 
and  a  graphical  presentation  of  the  closeness  of  fit  secured  are  con- 
tained in  Figs.  10  and  11.  The  junction  of  the  two  curves  for  each 


118 


BULLETIN  No.  278 


[June. 


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THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


119 


120  BULLETIN  No.  278  [June, 

set  of  data  has  no  mathematical  significance.  The  use  of  Robertson's 
growth  curve  in  this  way  obviously  is  purely  empirical. 

The  equations  obtained  in  this  manner  have  been  used  in  estimat- 
ing the  ages  at  which  even  pound  weights  are  attained  by  White  Ply- 
mouth Rock  birds  according  to  the  Illinois  and  the  Purdue  data.  The 
results  thus  secured  are  given  in  Table  37.  The  average  time  re- 
quired to  make  successive  pound  gains  in  weight  have  been  computed 
from  the  data  in  Table  37  and  compiled  in  Table  38. 

From  the  data  shown  in  Table  35,  i.  e.,  the  composition  of  suc- 
cessive pound  gains  in  weight,  and  in  Table  38,  the  average  time  re- 
quired to  make  successive  pound  gains  in  weight,. the  daily  retention 
of  protein,  ash,  and  energy  has  been  computed.*  Table  39  contains 
these  results.  In  applying  the  results  of  the  computed  composition 
of  successive  gains  in  weight  to  the  Purdue  growth  data,  the  assump- 
tion is  made  that  the  composition  of  a  bird  at  a  given  weight  is  not 
appreciably  dependent  on  the  time  required  to  reach  that  weight;  in 
other  words,  that  it  is  largely  independent  of  the  age  of  the  bird.  This 
assumption  is,  of  course,  only  approximately  true.  However,  the  re- 
sults obtained  in  this  experiment  bear  out  this  assumption,  particu- 
larly the  close  agreement  in  composition  between  the  two  groups  of 
1-pound  birds  killed  two  weeks  apart.  It  must  be  admitted,  however, 
that  the  results  in  Table  39  based  upon  the  Illinois  growth  data  are 
open  to  the  criticism  that  the  growth  secured  was  apparently  subnor- 
mal, while  the  results  based  on  the  Purdue  data  are  open  to  the  criti- 
cism that  the  assumption  just  considered  has  not  been  firmly  estab- 
lished, especially  for  birds  of  the  same  weight  but  differing  widely  in  age. 

The  abnormally  large  daily  retention  of  protein,  ash,  and  energy 
for  cockerels  weighing  2.5  pounds,  indicated  by  a  computation  based 
upon  the  Purdue  growth  data,  may  be  explained  from  the  fact  that  in 
the  Purdue  experiment  the  cockerels  and  pullets  were  not  separated 
until  the  tenth  week  of  age.  The  Illinois  growth  data  indicate  that 


'Obviously,  in  computing  the  average  daily  retention  of  nutrients  up  to  1 
pound  in  weight,  the  composition  of  the  gain  from  0  to  1  pound,  as  given  in 
Table  35,  must  be  corrected  for  the  composition  of  the  bird  at  hatching.  As- 
suming the  hatching  weight  of  White  Plymouth  Rock  birds  to  be  38  grams, 
based  upon  the  Purdue  data,  their  composition  in  grams  may  be  computed  by 
means  of  the  parabolic  equations  deduced  from  our  own  chemical  data,  with 
the  following  results: 

Dry  Crude  Crude  Gross 

matter  protein  fat  Ash  energy 

Calculated 10.56  •     6.83  1.97  1.10             47 

Observed 9.46  6.15  2.13  0.70             56 

The  observed  values  given  in  this  tabulation  are  computed  from  the  average 
composition  of  5  White  Rock  chicks  averaging  1V£  days  in  age  (Table  32).  The 
calculated  daily  retention  of  nutrients  of  .5-pound  chicks  is  therefore  based  upon 
the  estimated  composition  of  1-pound  chicks  minus  this  estimate  of  the  com- 
position of  chicks  shortly  after  hatching. 


1926] 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


121 


TABLE  37. — AVERAGE  AGES  AT  WHICH  EVEN  POUND  WEIGHTS  ARE  REACHED  BY 
WHITE  PLYMOUTH  ROCK  BIRDS 


] 

llinois  dati 

l 

] 

'urdue  dat 

a 

Cockerels 

Pullets 

Capons 

Cockerels 

Pullets 

Capons 

Ibs. 
1  

days 
54 

days 
60 

days 

days 
49a 

days 
49a 

days 

2  

101 

112 

102 

73a 

73a 

3  

140 

158 

140 

88 

105 

92 

4  

177 

223 

177 

111 

135 

114 

5.... 

221 

221 

135 

175 

135 

6... 

305 

304 

164 

260 

158 

7  

187 

8  

242 

aThe  cockerels  and  pullets  were  not  separated  in  the  Purdue  experiment  until 
the  tenth  week. 

cockerels  grow  faster  than  puilets  even  in  the  earlier  weeks  of  life,  so 
that  the  abnormally  rapid  gain  apparently  put  on  by  the  Purdue  cock- 
erels in  the  period  immediately  succeeding  their  separation  from  the 
pullets  is  probably  a  great  exaggeration  of  the  actual  gain. 

The  daily  retention  of  protein  by  growing  cockerels  averages  a 
little  over  2  grams  according  to  the  Illinois  growth  data,  and  about 
twice  as  much  according  to  the  Purdue  growth  data.  The  daily  re- 
tention of  mineral  matter  varies  from  .2  to  .5  gram  in  one  series,  and 
from  .3  to  about  1  gram  in  the  other.  The  daily  retention  of  energy 
increases  in  both  sets  of  data  from  10  to  12  calories  to  27  calories  in 
the  Illinois  estimates,  and  to  44  calories  according  to  the  Purdue  esti- 
mates (neglecting  the  abnormal  figure  for  the  2.5-pound  birds) ;  after 
which  a  decrease  in  the  rate  of  retention  occurs  according  to  the  Illi- 
nois growth  data.  The  Purdue  growth  data  indicate  a  sustained  max- 
imum retention. 

For  the  pullets  and  capons  a  slightly  smaller  daily  retention  of 
protein  and  mineral  matter  is  indicated  than  for  the  cockerels.  Altho 

TABLE  38. — AVERAGE  TIME  REQUIRED  BY  WHITE  PLYMOUTH  ROCK  BIRDS  TO  MAKE 
SUCCESSIVE  POUND  GAINS  IN  WEIGHT 


Gains 

Illinois  data 

Purdue  data 

Cockerels 

Pullets 

Capons 

Cockerels 

Pullets 

Capons 

Ibs. 
Hatching  to  1  
Ito2  

days 
54 
47 
39 
37 
44 
84 

days 
60 
52 
46 
65 

days 

'38 
37 
44 
83 

days 
49 
24 
15 
23 
24 
29 

days 
49 
24 
32 
30 
40 
85 

days 

'i9 
22 
21 
23 
29 
55 

2  to  3  

3  to  4  

4  to  5  

5  to  6  

6  to  7  

7  to  8  

122 


BULLETIN  No.  278 


[June, 


the  gains  on  the  pullets,  especially  at  the  higher  weights,  contained 
more  energy  than  the  gains  on  the  cockerels,  this  is  almost  exactly 
offset  by  the  slower  rate  at  which  the  pullets  grew,  so  that  little  con- 
sistent difference  is  evident  in  the  daily  retention  of  energy  by  cock- 
erels and  pullets.  The  greater  energy  content  of  the  gains  of  capons 
as  compared  with  cockerels  is  not  offset  by  a  slower  growth,  so  that  the 
values  in  Table  39  indicate  a  larger  daily  retention  of  energy  by  ca- 
pons than  by  cockerels  of  like  weight. 


TABLE  39. — DAILY  RETENTION  OF  PROTEIN,  ASH,  AND  ENERGY  BY  WHITE  PLYMOUTH 
ROCK  BIRDS  OF  DIFFERENT  WEIGHTS 


Kind  of  bird 
and  weight 

Illinois  data 

Purdue  data 

Age 

Protein 

Ash 

Energy 

Age 

Protein 

Ash 

Energy 

COCKERELS 
Ibs. 
0.5  

days 
34 
89 
122 
158 
197 
250 

34 
85 
132 
183 

gms. 
1.42 
1.88 
2.39 
2.65 
2.34 
1.28 

1.24 
1.69 
2.06 
1.56 

gms. 
0.23 
0.32 
0.43 
0.49 
0.44 
0.25 

0.21 
0.27 
0.32 
0.23 

cals. 
10.5 
15.9 
22.5 
27.3 
25.9 
15.2 

9.6 
17.5 
26.0 
22.9 

days 
32 
61 
75 
99 
122 
148 

32 
62 
89 
120 
153 
204 

80 
103 
124 
146 
172 
209 

gms. 
1.57 
3.68 
6.21 
4.26 
4.28 
3.71 

1.52 
3.66 
2.96 
3.38 
2.70 
1.35 

4.59 
3.98 
4.20 
3.86 
3.08 
1.63 

qms. 
0.26 
0.63 
1.11 
0.79 
0.81 
0.72 

0.26 
0.59 
0.45 
0.49 
0.38 
0.18 

0.75 
0.62 
0.61 
0.53 
0.39 
0.19 

cals. 
11.6 
31.1 
58.5 
43.9 
47.5 
43.9 

11.8 
37.9 
37.4 
49.5 
44.3 
24.2 

54.0 
54.7 
65.8 
67.8 
59.9 
34.8 

1.5  

2.5  

3.5  

4.5  

5.5  

PULLETS 
Ibs. 
0.5  

1.5  

2.5  

3j5  

4.5  

5.5  

CAPONS 
Ibs. 
2.5  

120 
157 
195 
249 

2.29 
2.37 
2.00 
1.07 

0.38 
0.37 
0.29 
0.15 

27.0 
32.5 
31.4 

18.8 

3.5  .. 

4.5  

5.5  

6.5  

7.5  

It  is  of  interest  to  compare  the  rate  of  retention  of  protein  by 
growing  White  Plymouth  Rock  chickens  with  the  rate  of  retention  of 
protein  by  other  species  of  farm  animals.  Armsby13  has  made  an  ex- 
tensive compilation  of  such  data  for  cattle,  sheep,  and  swine,  and  has 
found  that  when  the  daily  retention  is  expressed  in  terms  of  gain  of 
protein  per  1,000  pounds  live  weight  per  day,  the  change  in  rate  of 

135 

retention  is  fairly  well  represented  by  the  equation,  a  = ;  in 

a-f-20 

which  g  is  the  gain  of  protein  in  pounds  per  day  per  1,000  pounds  live 
weight,  and  a  is  the  age  in  days.     This  equation  corresponds  fairly 


1926} 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS 


123 


well  with  the  general  average  of  the  observed  results  on  cattle  and 
sheep,  especially  for  the  later  ages.  With  swine  the  few  results 
available  appear  to  indicate  a  greater  rate  of  protein  retention  during 
the  first  three  months  than  would  be  predicted  from  this  equation. 

A  comparison  of  the  daily  retention  of  protein  per  pound  of  live 
weight  calculated  from  this  equation,  with  the  daily  retention  of  pro- 

TABLE  40. — CALCULATED  AND  OBSERVED  DAILY  RETENTION  OF  PROTEIN  PER  POUND 
LIVE  WEIGHT  BY  WHITE  PLYMOUTH  ROCK  COCKERELS 


Body  weight 

Illinois  data 

Purdue  data 

Protein  retention  per  day 
per  pound  body  weight 

Protein  retention  per  day 
per  pound  body  weight 

Age 

Observed 

Calculated8 

Age 

Observed 

Calculated3 

Jbs. 
0.5 

days 
34 

gms. 

2.84 

gms. 
1.13 

days 
32 

gms. 
3.14 

gms. 
1.18 

1.5 

89 

1.25 

0.56 

61 

2.45 

0.76 

2.5 

122 

0.96 

0.43 

75 

2.48 

0.64 

3.5 

158 

0.76 

0.34 

99 

1.22 

0.52 

4.5 

197 

0.52 

0.28 

122 

0.95 

0.43 

5.5 

250 

0.23 

0.21 

148 

0.68 

0.36 

''The  estimated  protein  retention  was  calculated  by  the  use  of  Armsby's  general- 
ized equation  given  on  page  378  of  "The  Nutrition  of  Farm  Animals." 

tein  as  computed  from  the  Illinois  analyses  and  growth  data  on  White 
Plymouth  Rocks,  and  also  from  the  growth  data  reported  from  Purdue, 
appears  in  Table  40.  The  rate  of  gain  of  protein  by  growing  White 
Plymouth  Rock  cockerels  is  two  to  three  times  as  rapid  as  that  pre- 
dicted from  Armsby's  equation  deduced  from  data  for  larger  farm  ani- 
mals. 

A  comparison  of  the  rate  of  gain  of  energy  by  White  Ply- 
mouth Rock  cockerels  and  by  growing  calves  may  be  made  using 
Armsby's  estimates  of  the  rate  of  gain  of  energy  per  day  and  per 

TABLE  41. — ESTIMATED  RATE  OF  GAIN  OF  ENERGY  PER  DAY  PER  POUND  LIVE 

WEIGHT  OF  WHITE   PLYMOUTH   ROCK  COCKERELS  AS  COMPARED   WITH 

ARMSBY'S  SIMILAR  ESTIMATES  FOR  CALVES  OF  LIKE  AGES 


Illinois  data 


Energy  retained  daily  per 
pound  live  weight 

Energy  retained  daily  per 
pound  live  weight 

Age 

Cockerels 

Calves* 

Age 

Cockerels 

Calves8 

days 
34 
89 
122 
158 
197 
250 

cals. 
21.0 
10.6 
9.0 

7.8 
5.8 
2.8 

cals. 
17.4 
11.1 
8.9 
7.1 
5.6 
5.0 

days 
32 
61 
75 
99 
122 
148 

cals. 
23.2 
20.7 
23.4 
12.5 
10.5 
8.0 

cals. 
17.6 
13.4 
12.2 
10.4 
8.9 
7.6 

Purdue  data 


"The  estimates  for  calves  were  obtained  by  simple  interpolation  from  Table  94, 
page  402,  of  Armsby's  "The  Nutrition  of  Farm  Animals." 


124  BULLETIN  No.  278  [June, 

1,000  pounds  live  weight  by  calves  of  different  ages.14  While  Armsby 
also  estimates  the  rate  of  gain  of  energy  by  swine,  his  estimates  can- 
not be  considered  reliable,  because  of  the  small  amount  of  data  upon 
which  they  are  based  and  because  of  discrepancies  existing  among  them. 
In  Table  41  the  rate  of  gain  of  energy  made  by  White  Ply- 
mouth Rock  cockerels,  per  pound  of  live  weight,  at  increasing  ages, 
is  compared  with  Armsby's  estimated  rates  of  gain  of  energy  by  calves 
per  pound  of  live  weight.  The  estimates  for  calves  included  in  each 
comparison  have  been  obtained  from  Armsby's  Table  94  by  simple 
interpolation.  Except  for  the  earliest  and  the  latest  age,  a  remark- 
ably close  agreement  exists  between  the  estimated  rate  of  gain  of  en- 
ergy of  WThite  Plymouth  Rock  cockerels  computed  from  the  Illinois 
growth  data  and  the  estimated  rate  of  gain  of  energy  by  calves  of 
equal  age.  For  the  estimates  based  upon  the  Purdue  growth  data  no 
close  agreement  exists  with  Armsby's  estimates  at  equal  ages. 

SUMMARY  AND  CONCLUSIONS 

An  investigation  of  the  growth  of  White  Plymouth  Rock  chick- 
ens was  made,  involving  observations  of  the  increase  in  live  weight, 
the  increase  in  body  measurements,  the  increase  in  weight  of  individ- 
ual organs  and  parts  of  the  carcass,  and  the  changing  chemical  compo- 
sition of  the  carcass  and  of  gains  in  weight  with  increase  in  size. 

The  growth  and  body  weight  of  a  flock  of  White  Plymouth  Rock 
chickens  numbering  approximately  1,000  at  the  beginning  of  the  ex- 
periment was  determined  by  weighing  the  birds  individually  every 
two  weeks.  The  growth  of  cockerels  and  pullets  was  observed  sep- 
arately as  soon  as  the  sex  could  be  distinguished.  When  the  cockerels 
reached  an  age  of  10  weeks,  approximately  half  of  them  were  capon- 
ized,  and  from  this  time  constituted  a  third  group  of  birds.  The  rate 
of  growth  as  measured  by  the  biweekly  increase  in  body  weight  was 
found  to  vary  periodically.  These  variations,  however,  have  not  been 
interpreted  as  representing  true  cycles  of  growth,  because  it  is  believed 
that  they  more  probably  are  related  to  periodical  variations  in  en- 
vironmental conditions,  particularly  variations  in  the  weather. 

Relative  Growth  of  Cockerels,  Capons,  and  Pullets. — The  growth 
of  the  cockerels  proceeded  at  a  distinctly  more  rapid  rate  than  that  of 
the  pullets,  even  from  the  time  when  the  separation  was  first  made. 
The  rate  of  growth  of  the  capons  was  not  distinctly  different  from  that 
of  the  cockerels  up  to  a  weight  of  approximately  6  pounds.  All  groups 
of  birds  grew  at  a  much  slower  rate  than  the  Purdue  flock  reported 
upon  in  Bulletin  214  from  that  station. 

From  a  study  of  the  change  in  the  ten  body  measurements  with 
advancing  age,  it  appears  that  practically  all  of  the  measurements  in- 
creased in  approximately  the  same  proportion  when  referred  to  the 


THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS  125 

measurements  of  the  .5-pound  chicks.  Thus,  for  the  cockerels,  all  the 
measurements  except  the  length  of  middle  toe  increased  approximately 
two  and  a  half  times  from  the  .5-pound  to  the  7-pound  weight.  This 
would  appear  to  mean  that  the  conformation  of  the  birds  did  not 
change  materially  during  the  whole  course  of  growth  between  these 
two  extreme  weights. 

At  equal  weights  the  pullets  were,  in  general,  smaller  in  external 
measurement  than  the  cockerels,  the  only  measurement  remaining  ap- 
proximately the  same  in  the  two  sexes  being  the  length  of  keel.  The 
leg  measurements  of  the  pullets  in  particular  were  appreciably  smaller 
than  those  of  the  cockerels  of  like  weight,  especially  after  a  weight  of 
3  pounds  was  reached. 

On  the  other  hand,  no  distinct  differences  between  the  body  meas- 
urements of  capons  and  cockerels  at  equal  weights  were  revealed. 
Castration  apparently  does  not  appreciably  affect  the  body  shape  of 
White  Plymouth  Rock  cockerels. 

Estimating  Surface  Area. — The  surface  area  of  all  birds  slaugh- 
tered in  this  experiment  was  directly  determined  by  measuring  the 
area  of  the  skin  after  removal  from  the  carcass.  In  attempting  to  find 
a  formula  by  which  the  body  surface  of  White  Plymouth  Rock  chick- 
ens could  be  estimated  readily,  it  was  found  that  the  Meeh  formula 
could  not  be  used  over  the  entire  range  of  weight  from  .5  to  7  pounds. 
However,  the  Meeh  formula  may  be  applied  with  considerable  accur- 
acy to  birds  weighing  more  than  1  pound,  using  the  value  of  9.85  for 
the  constant,  the  area  being  expressed  in  square  centimeters  and  the 
weight  in  grams.  A  slightly  more  accurate  formula,  which  may  be 
used  for  birds  weighing  from  1  to  7  pounds,  inclusive,  was  devised  by 
the  use  of  one  of  the  body  measurements,  namely,  the  rump-to-shoulder 
measurement,  along  with  the  body  weight.  This  formula  is  as  follows: 

S  =  5.86  W-5  L-« 

in  which  S  is  the  surface  area  in  square  centimeters,  W,  the  weight  in 
grams,  and  L,  the  rump-to-shoulder  distance  in  centimeters.  This  for- 
mula also  applies  to  Rhode  Island  Red  chickens,  but  evidently  does 
not  apply  to  White  Leghorns  unless  the  constant  is  made  smaller  (i.e., 
5.03). 

Growth  of  Different  Parts  of  Carcass  and  Viscera. — From  a  study 
of  the  weights  of  the  different  organs  and  the  different  parts  of  the 
carcass,  it  is  evident  that  most  of  these  increase  in  weight  continuously 
with  advancing  age.  The  digestive  organs,  however,  are  somewhat  ex- 
ceptional in  their  growth,  since  they  reach  their  maximum  size  before 
the  bird  has  obtained  its  complete  growth. 

The  offal  part  of  the  carcass,  not  including  the  inedible  viscera, 
was  found  to  constitute  a  fairly  constant  percentage  of  the  empty 
weight  of  the  birds  at  all  weights,  namely,  very  close  to  19  per- 
cent. This  constancy  in  percentage  weight  holds  particularly  for  the 
blood  weights.  The  percentage  weight  of  blood  is  consistently  higher 


126  BULLETIN  No.  278  [June, 

for  the  cockerels  than  for  the  pullets.  The  capons  occupy  an  inter- 
mediate position  in  this  respect. 

Following  an  initial  increase  from  the  .5-pound  to  the  1 -pound 
chicks,  the  percentage  weight  of  the  total  viscera  showed  a  continuous 
decrease  with  increasing  weight  of  birds.  This  conforms  with  similar 
data  on  man  and  other  mammals. 

The  percentage  weight  of  the  total  dressed  carcass  increased 
slightly,  but  continuously,  with  increasing  empty  weight  of  the  bird. 
This  relative  increase  in  dressed  carcass  relates  more  to  the  muscular 
tissue  than  to  the  bones.  For  all  three  groups  of  birds  the  percentage 
weight  of  bone  in  the  dressed  carcass  decreased  with  increasing  body 
weight,  while  the  percentage  weight  of  flesh  and  fat  increased. 

The  total  weights  of  offal  were  consistently  less  for  the  pullets 
than  for  the  cockerels  of  like  weight.  This  is  true  of  each  item  in  the 
offal,  except  the  feathers.  The  weights  of  feathers  for  the  pullets 
were  generally  greater  than  those  for  the  cockerels.  While  the  total 
weights  of  viscera  did  not  differ  greatly  for  cockerels  and  pullets,  some 
apparently  significant  differences  existed  between  the  two  sexes  rela- 
tive to  individual  organs.  For  example,  at  a  weight  of  2  pounds  the 
lungs  of  the  pullets  weighed  the  same  as  the  lungs  of  the  cockerels,  but 
with  increasing  body  weight  the  lungs  of  the  cockerels  weighed  more 
than  those  of  the  pullets,  the  differences  increasing  with  increasing 
body  weight.  Just  the  reverse  is  true  with  the  kidneys.  The  weights 
of  spleen  were  consistently  heavier  for  the  pullets  than  for  the  cock- 
erels. The  dressed  carcass  in  the  pullets  was  always  slightly  heavier 
than  in  the  cockerels  for  body  weights  of  3  pounds  or  more,  altho  the 
weights  of  bone  in  the  dressed  carcass  were  always  greater  at  the 
same  body  weight  for  cockerels  than  for  pullets.  In  other  words,  the 
edible  flesh  and  fat  always  constituted  a  greater  percentage  of  the 
empty  weight  of  the  pullets  than  of  the  cockerels  of  equal  weight. 

Differences  between  cockerels  and  capons  relative  to  the  weights 
of  the  different  parts  of  the  body  were  not  so  numerous  nor  so  con- 
sistent as  those  between  cockerels  and  pullets.  However,  at  a  weight 
of  7  pounds  some  interesting  differences  apparently  existed.  The 
heart  weights  were  distinctly  greater  for  the  cockerels  than  for  the 
capons  at  this  weight,  while  the  weights  of  liver,  kidney,  spleen,  and 
intestines  for  the  capons  were  distinctly  greater  than  for  the  cockerels. 
The  average  weights  of  kidney  and  spleen  were  greater  for  the  capons 
than  for  the  cockerels  at  all  weights.  Apparently  castration  pro- 
foundly affected  the  growth  of  these  visceral  organs. 

Chemical  Composition  of  Birds. — The  data  relating  to  the  chemi- 
cal composition  of  the  birds  showed  the  changes  in  dry  matter,  pro- 
tein, ash,  fat,  and  energy  with  increasing  age  that  would  be  expected 
from  similar  studies  on  other  animals.  Comparing  the  three  groups 
of  birds,  the  analyses  show  that  the  pullets  fattened  distinctly  more 


1926]  THE  GROWTH  OF  WHITE  PLYMOUTH  ROCK  CHICKENS  127 

rapidly  than  the  cockerels,  while  the  capons  occupied  an  intermediate 
position.  The  energy  values  per  gram  of  tissue  for  the  pullets  for 
weights  above  3  pounds  were  always  distinctly  higher  than  the  energy 
values  for  either  cockerels  or  capons.  The  energy  values  of  all  samples 
obtained  in  this  experiment  were  directly  determined  by  means  of  the 
bomb  calorimeter. 

The  distribution  of  nutrients  between  the  three  composite  samples 
analyzed  in  this  experiment, — namely,  (1)  the  flesh  and  edible  viscera, 
(2)  the  bones  of  the  dressed  carcass,  and  (3)  the  head,  shanks  and 
feet,  blood,  feathers,  and  non-edible  viscera  (conveniently  referred  to 
as  the  offal), — did  not  show  any  progressive  changes  with  advancing 
age.  The  flesh  and  edible  viscera  contained  on  an  average  35.5  percent 
of  the  total  dry  matter,  40.8  percent  of  the  total  protein,  30.2  percent 
of  the  total  fat,  37.2  percent  of  the  total  gross  energy,  and  14.7  per- 
cent of  the  total  ash  of  the  entire  carcass. 

At  equal  live  weights,  pullets  contained  more  edible  fat  and  en- 
ergy and  as  much  edible  protein  as  cockerels,  the  difference  with  re- 
spect to  fat  and  energy  increasing  rapidly  with  increasing  live  weight. 
Capons,  at  equal  weights,  contained  amounts  of  edible  fat  and  energy 
midway  between  cockerels  and  pullets,  and  smaller  amounts  of  edible 
protein  than  either. 

From  the  analysis  of  these  three  composite  samples  the  composi- 
tion of  the  live  birds  at  the  different  weights  was  computed,  and  from 
these  figures,  the  weights  of  chemical  constituents  contained  in  birds 
weighing  exactly  0.5,  1.0,  1.5,  2.0,  3.0  pounds,  etc.  To  render  more 
accurate  the  subsequent  calculations  of  the  composition  of  successive 
pound  gains  in  weight,  the  experimental  data  on  the  composition  of 
birds  at  definite  weights  were  smoothed  out  by  fitting  to  them  para- 
bolic equations  of  the  general  type, 

y  =ax  -\-  bx2 

'the  constants  being  determined  by  the  method  of  least  squares.  From 
the  equations  thus  obtained  the  composition  of  birds  at  even  pound 
weights  was  estimated,  and  from  these  estimations  the  composition  of 
successive  pound  gains  in  weight  was  determined. 

Rate  of  Retention  of  Nutrients  During  Growth. — In  computing 
the  daily  retention  of  nutrients  by  birds  of  different  ages,  the  data  on 
the  corrected  composition  of  successive  gains  and  the  data  on  the 
growth  and  body  weight  of  the  entire  flock  of  birds  were  used. 
The  latter  were  also  smoothed  out  by  mathematical  means  in  a  purely 
empirical  fashion.  Since,  however,  the  growth  of  the  flock  of  birds 
used  in  this  experiment  was  considerably  slower  than  the  growth 
of  White  Plymouth  Rock  chickens  reported  from  the  Purdue  Ex- 
periment Station  by  Philips,  two  sets  of  values  on  the  daily  reten- 
tion of  nutrients  were  computed,  applying  the  values  on  the  composi- 


128  BULLETIN  No.  278  {June, 

tion  of  successive  gains  to  both  the  Illinois  and  the  Purdue  corrected 
growth  data. 

The  daily  retention  of  protein  by  White  Plymouth  Rock  cockerels 
evidently  ranges  between  2  grams  and  4.5  grams  per  day,  depending 
upon  whether  they  are  growing  at  their  maximum  rate  or  at  a  slower 
and  probably  more  nearly  average  rate  for  birds  on  the  farm.  Except 
for  smaller  figures  for  the  first  two  months  of  growth  and  a  slowing 
up  of  growth  as  maturity  is  approached,  no  marked  change  in  the 
daily  retention  of  protein  at  increasing  ages  was  noted.  The  daily 
retention  of  protein  by  pullets  and  capons  was  less  than  that  for  cock- 
erels. The  daily  retention  of  mineral  matter  by  White  Plymouth 
Rock  cockerels  ranges  between  .2  gram  and  1  gram  per  head,  with  no 
clear  progressive  variation  except  for  the  early  ages  up  to  a  weight  of 
2.5  pounds.  The  maximum  retention  of  mineral  matter  was  established 
at  a  level  of  .5  to  .8  gram  daily.  The  daily  retention  of  minerals  by 
pullets  and  capons  appeared  to  be  distinctly  less  than  that  by  cock- 
erels. 

The  estimates  of  the  daily  retention  of  energy  by  growing  cock- 
erels were  quite  variable  at  different  ages,  showing  no  progressive 
changes  after  a  weight  of  2.5  pounds  was  reached.  The  average  daily 
rate  of  gain  of  energy  from  2.5  pounds  upward  was  about  25  calories 
according  to  the  Illinois  growth  data,  and  about  45  to  50  calories  ac- 
cording to  the  Purdue  growth  data. 

Between  pullets  and  cockerels  no  differences  in  the  rate  of  reten- 
tion of  energy  were  apparent,  tho  for  capons,  the  daily  retention  of 
energy  was  consistently  higher  than  for  cockerels. 

LITERATURE  CITED 

1.  ARMSBY,  H.  P.  The  nutrition  of  farm  animals,  p.  400.   Macmillan.    1917. 

2.  PURDUE  AGR.  EXP.  STA.    Bui.  214. 

3.  HOGAN,  A.  G.,  and  SKOUBY,  C.  I.   Journ.  Agr.  Res.  25,  419-430.   1923. 

4.  JACKSON,  C.  M.  Amer.  Journ.  Anat.  15,  1.   1913-14. 

5.  DONALDSON,  H.  H.  Amer.  Jour.  Physiol.  67,  1.   1923-24. 

6.  DONALDSON,  H.  H.    Trans.  15th  Internatl.  Cong.  Hyg.  and  Demog.    Wash- 

ington, D.  C.    1912. 

7.  MARRASSINI,  A.,  and  LUCIANI,  L.  Arch.  Ital.  Biol.  56,  395.   1911-12. 

8.  HATAI,  S.   Anat.  Rec.  9,  647.   1915. 

9.  HOSKINS,  R.  G.   Amer.  Jour.  Physiol.  72,  324.    1925. 

10.  RICHTER,  C.  P.  Johns  Hopkins  Hosp.   Rpts.  36,  324.    1925. 

11.  KEMPSTER,  H.  L.,  and  HENDERSON,  E.  W.    Normal  growth  of  domestic  ani- 

mals.   Mo.  Agr.  Exp.  Sta.    Res.  Bui.  62,  40.    1923. 

12.  ROBERTSON,  T.  B.    The  chemical  basis  of  growth  and  senescence.    Lippincott. 

1923. 

13.  ARMSBY,  H.  P.    The  nutrition  of  farm  animals,  p.  378.    Macmillan.    1917. 

14.  AUMSBY,  H.  P.    The  nutrition  of  farm  animals,  p.  402.    Macmillan.    1917. 


1926] 


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